Design Note 428: Tiny Synchronous Step-Up Converter Starts Up at 700mV. Aaa battery voltage curve

Design Note 428: Tiny Synchronous Step-Up Converter Starts Up at 700mV

Alkaline batteries are convenient because they’re easy to find and relatively inexpensive, making them the power source of choice for portable instruments and devices used for outdoor recreation. Their long shelf life also makes them an excellent choice for emergency equipment that may see infrequent use but must be ready to go on a moment’s notice. It is important that the DC/DC converters in portable devices operate over the widest possible battery voltage range to extend battery run time, and thus save the user from frequent battery replacement.

Single-cell alkaline batteries, with a 1.6V to 0.9V range, present a special challenge to DC/DC converters because of their low voltage and the fact that their internal resistance increases as the battery discharges. Thus, a DC/DC converter that can both start up and operate efficiently at low input voltages is ideally suited for single-cell alkaline products.

The LTC3526L is a 1MHz, 550mA synchronous stepup (boost) converter with a wide input voltage range of 0.7V to 5V and an output voltage range of 1.5V to 5.25V. Housed in a 2mm × 2mm DFN package, the LTC3526L has a typical startup voltage of just 700mV, with operation down to 400mV once started. Despite the LTC3526L’s tiny solution size, it includes many advanced features, including output disconnect, short circuit protection, low noise fixed frequency operation, internal compensation, soft-start, thermal shutdown and Burst Mode ® operation for high efficiency at light load. For low noise applications, the LTC3526LB offers fixed frequency operation at all load currents. With an output voltage range that extends down to 1.5V, the LTC3526L and LTC3526LB can even be used in applications previously requiring a boost converter followed by a buck converter.

A typical single-cell boost application is shown in Figure 1. In this example the LTC3526LB is used to generate 1.8V for a Bluetooth radio application. The LTC3526LB was selected for its small size, minimal external component count and low-noise, fixed frequency operation at all load currents. A graph of output current capability versus input voltage is shown in Figure 2. Note that the converter starts up at 700mV at no load and once running, can deliver 25mA of output current with an input voltage of only 400mV. The 1MHz switching frequency allows the use of small, low profile inductors, such as the monolithic chip inductor shown in this application. This provides a complete solution with a footprint that’s just 36mm 2 with a 1mm profile.

Many new battery types are available to the consumer, some of which are aimed at high-tech, high power applications. One of these is the disposable lithium AA/AAA battery, which offers a significant improvement in runtime over traditional alkaline batteries. Furthermore, in applications that see infrequent use, the long shelf life of lithium batteries gives them a performance edge over nickel-based rechargeable batteries, which have a high self-discharge rate.

One characteristic of the lithium battery is that its voltage can be as high as 1.8V when the battery is fresh, compared to 1.6V for a typical alkaline battery. This is a problem for 2-cell alkaline applications that use a traditional boost converter to produce a 3.3V output from an alkaline 3.2V max input. Most boost converters cannot maintain regulation when the input is higher than the output, as it is with two fresh lithium batteries (3.6V).

The LTC3526L solves this problem by maintaining regulation even when the input voltage exceeds the output voltage. An example of a 2-cell to 3.3V boost converter using the LTC3526L is shown in Figure 3. A small feed-forward capacitor has been added across the upper divider resistor to reduce output ripple in Burst Mode operation. Efficiency vs load curves are shown in Figure 4. These curves demonstrate the high efficiency at light load made possible by the low 9μA quiescent current of Burst Mode operation. The curve in Figure 5 illustrates the efficiency at input voltages above and below the output voltage.

Conclusion

The LTC3526L is a highly integrated step-up DC/DC converter in a 2mm × 2mm package designed to easily fit a wide variety of battery-powered applications. Low startup and operating voltages extend runtime in single-cell applications. It even regulates in step-down situations where the fresh battery voltage (VIN) may exceed VOUT. For high efficiency at light loads, or low noise operation, it offers a choice of Burst Mode or fixed frequency operation.

Author

David Salerno was a Design Section Leader for the Power by Linear group of Analog Device (former Linear Technology) for nearly 20 years. His main FOCUS was the DC/DC Converter design on boost applications. David hold an BSEE from the Purdue University since 1978. He retired May 2019.

ENELOOP RECHARGEABLE BATTERIES, THE BEST!

A list of eneloop test results with extra explanation and/or critique.

ENELOOP vs ALKALINE BATTERIES (Fujitsu)

Rechargeable batteries used to be pretty bad at keeping their charge, and still till today Alkaline batteries are very cheap. But each brand has its pros and cons.

Please have a look to understand the difference between basic Eneloop batteries vs Alkaline batteries. Alkaline batteries have a large capacity at very low current. Whenever the device pulls more current the Alkaline batteries supply much less energy than eneloops. Take a look at the following comparison between a Fujitsu High Power AA and one of the best rechargeable batteries, the standard AA Eneloop 4th generation.

• Compare mAh at 0,1A:This is a low current. Clocks will use an even smaller current. An Alkaline Fujitsu battery has a capacity of 2258mAh, while an eneloop can provide 1859mAh according to HKJ`s tests. So the Alkaline can run longer on very low currents.
• Compare mAh at 1A:With devices that pull more current the eneloop batteries really show their strength. The Fujitsu AA Alkaline can only provide 564mAh at this current while the eneloop still shows 1785 mAh.
• Compare mAh at 3A:Fujitsu Alkaline now gives about 426mAh while the eneloop gives 1736mAh.

Short Conclusion: Alkaline batteries can have an advantage in very low current devices like clocks and remote controls. But at the same time come with a very big disadvantage that they can leak and destroy almost any device.

ENELOOP CAPACITY TESTS

HKJ is a member on forums like Candlepowerforums and Budgetlightforums and has done over 1000 tests on batteries, chargers, flashlights and other electronics. He is a very reliable source for reviews and comparisons.

Capacity tests

He uses a bench power supply that can be controlled by a computer to mainstream battery tests. With that he can both adjust Voltage and Current easily. To read more about his tests setup, take a look at his website I will be linking to in the next few tests. Please note that eneloop batteries have the highest capacity after about 3-5 charges.

There are always slight different readings as well depending on the ambient temperature etc.

As you can see, that eneloop batteries can handle a much higher current than Alkalines. You can notice the slight decrease in capacity when the current increases. But even at 3A or 5A they still prove a strong contender. So the best rechargeable batteries can’t be beaten by Alkalines at higher current.

AA STANDARD MODEL CAPACITY TEST

Eneloop standard 3rd generation:

Take a look at the table and look for the Measured Capacity. 0,5A it has a capacity of about 1850 mAh. 2A it still has a capacity of 1790 mAh. And at 5A still 1718 mAh. Go to the complete review here.

Eneloop standard 4th generation:

Again, look at the numbers behind Measured Capacity for the mAh. 0.5A a capacity of about 1883 mAh. 2A it has a capacity of 1826 mAh. And at 5A= 1766 mAh, so even at 5A they hold up really really well! For the complete test by HKJ see here.

Eneloop std. 4th gen (2016 model):

See the Measured Capacity in mAh 0,5A it has a capacity of about 1809 mAh. At 2A it still has a capacity of 1760 mAh. Not tested at 5A this time. Go to the complete review by HKJ here.

AA PRO MODEL CAPACITY TEST

Eneloop Pro 3rd generation: 3UWXB

0.5A = 2431mAh, 1A = 2402mAh 5A= 2265mAh

For the complete test by HKJ see here.

Eneloop Pro 5th generation:

0.5A = 2430mAh 1A = 2401mAh 5A= 2286mAh

For the complete test by HKJ see here.

AA LITE MODEL CAPACITY TEST

Eneloop Lite 2nd generation: 3LCC

0.5A = 890mAh, 1A = 860mAh 3A= 789mAh (Not tested at 5A)

For the complete test by HKJ see here.

Eneloop Lite 2nd generation (Europe):

0.5A = 903mAh 1A = 878mAh 3A= 814mAh (not tested at 5A)

For the complete test by HKJ see here.

AAA ENELOOP CAPACITY TEST

Eneloop std 3rd generation: 4UTGB

0.5A = 714mAh, 1A = 706mAh 3A= 654mAh (Not tested at 5A)

For the complete test by HKJ see here.

Eneloop Pro 4th generation: 4HCC

0.5A = 888mAh 1A = 865mAh 3A= 738mAh

For the complete test by HKJ see here.

TRACKING OF CELLS (with a Voltage curve)

Eneloops are not only powerful high quality cells, they are consistent from cell to cell. Capacity wise and performance wise. This means that all batteries have the same power and performance without much variety/inconsistency. You can see the lines in the graphs being always very close to each other. They are very Consistent! Cheaper cells may have bigger capacity at SOME discharge current, but many times Fail to have identical performance, are less reliable or can`t handle higher discharge currents.

Look at this example of an eneloop AA test by HKJ. You can see both batteries are on the same line. They have the same performance.

If you then compare this with a GP AA test for example, which is also a pretty good battery, you can see the 2 lines (which indicate 2 batteries) still track well, but not as close.

And the following are some cheaper rechargeable batteries which even have a higher fluctuation.

You can see that the difference in performance between 2 cells when you look at the colored lines. So it is not only about max capacity it is about Consistent Performance!

REAL CAPACITY vs CLAIMED CAPACITY

Look at the following graph of a 2500mAh battery. Which by some people should have more capacity than a 1900mAh eneloop cell. Well, take a look and judge by yourself. Sanyo and Panasonic do real tests with real test results according to IEC and JIS standards, they don`t lie. But many companies lie about real capacity. These BTA are one of the worst batteries you can buy. They might have better quality cells at some point, but I stay away from them because of these business practices.

Rechargeable Batteries — compared and explained in detail (NiMH, NiZn, NiCd, RAM in AAA, AA, C, D, 9V sizes)

History. Until the late 1990’s, NiCd’s were the only option for rechargeable batteries in household sizes, but their capacity was terrible, and they contain toxic cadmium, which means they were supposed to be disposed of as hazardous waste, not in household trash. Around the turn of the century we were saved from this tyranny when NiMH’s became widely available, offering triple the capacity, and with non-hazardous materials, for about the same price. As a result, NiCD’s have all but disappeared.

Where to Buy. I like Amazon for most goods, because the are low and they stock everything. If you need them today then many grocery stores stock them, but the are often higher and the capacities lower then what you can get from more careful shopping. eneloops are good, and I have a separate page where I cover my recommended brands (as well as which to avoid).

High-Drain Performance. Devices that need lots of power quickly, like digital cameras, are called high-drain. That’s as opposed to devices that just sip the juice slowly, like clocks. NiMH work great in high-drain devices. In fact, many digital camera manufacturers recommend them, and even design their cameras for the lower voltage of the NiMH’s. An example of a battery that doesn’t work well in high-drain devices is a standard alkaline (though there are premium alkalines like Duracell Ultra that work fine in cameras, except they can’t be recharged).

Capacity. AA capacities range from 1200 to 2700 mAh. Beware of obscure brands that promise higher capacity—they usually deliver just a fraction of their label rating. (See my list of good and bad brands.) Also be sure to get a good charger because some cheaper ones don’t fill the batteries up completely. You might not get the label capacity right out of the box; good brands take 5-7 charge cycles to spec, though others take up to 100 cycles. You get peak capacity around 300 cycles. (BatteryU.) NiMH’s purportedly lose some of their capacity permanently if not used for long periods of time, but I haven’t been able to dig up any stats on how much. (Battery U.)

Self-Discharge. Normal NiMH’s have the highest self-discharge rate of any kind of battery (meaning they lose charge just by sitting around, unused), but there are Low Self-Discharge (LSD) versions available (like eneloop). The tradeoff is that the LSD versions have a little lower capacity. So when buying NiMH’s, you have to choose between longer shelf life or higher capacity. If you burn through batteries quickly, get the regular NiMH’s so you can enjoy the larger capacity. But if you go months before using up the battery’s capacity, go for LSD instead. The table at right shows the relationship between self-discharge and capacity.

One nice thing about the LSD versions is that they come pre-charged. Regular NiMH’s must be charged before use.

Voltage. NiMH’s are rated at 1.2V initial voltage, which is lower than the 1.5V that alkalines put out at first. This is generally not a problem, but it does mean that flashlights will be dimmer at first, and devices that need 4 or more batteries might burn through the batteries very quickly or not work at all. On the other hand, some devices (like many digital cameras) are designed to work with the lower 1.2V, so the reduced voltage is definitely not a problem there. If NiMH’s don’t supply enough voltage for your device, consider NiZn’s, or mixing NiMH and NiZn together, after seeing the caution about mixing NiMH and NiZn in the same device.

Voltage Drop. Like most other rechargeables, NiMH batteries maintain most of their voltage over the whole charge and then suddenly plummet. This contrasts to alkalines, which lose their capacity steadily. For this reason many electronic devices that tell you how much battery life is left have a hard time reporting an accurate level for NiMH’s. The voltage is very similar for both a fully-charged battery and a nearly-spent battery. Some devices (like my GPS wristwatch) let you specify in the setup menu whether you’re using NiMH or alkalines, so they can try to be more accurate with the battery-remaining indicator.

Charging. Overcharging can reduce cycle life (the number of times the battery can be charged). Smart chargers know when the battery is full and stop charging. Dumb chargers run on a timer and will almost always overcharge or fail to fill up the battery completely, and they usually really fail to fill up C and D sizes. Charging NiMH with old NiCd chargers is not recommended. (Modern chargers handle both NiMH’s NiCd’s.) Note that some Smart chargers are better than others, too.

I haven’t been able to find out whether you get more cycles but charging NiMH’s early vs. waiting until they’re deplated, but it probably doesn’t matter: You can typically charge NiMH’s hundreds of times without special care, so I wouldn’t worry about it, and suggest you just charge whenever you like.

An ideal charge rate is probably around 4-6 hours (for empty to full). Faster than that will work, but isn’t optimal. For slower charges, besides wasting time, there’s the possibility that a Smart charger will miss the cutoff signal that tells it to stop charging.

See the Charging Tips page for more about charging.

Cycle Life. NiMH’s are good for hundreds of charge cycles in theory, but overcharging and repeatedly running the batteries down all the way can reduce cycle life. To avoid overcharging, use a Smart charger that stops charging when the battery’s had enough. (See the chargers page for recommendations.) You’ll also get more cycles if you charge your batteries before they’re fully run down.

The original (2005) Sanyo Eneloop LSD’s were rated for 1000 cycles, and the newest ones are rated for 1500 and 1800 cycles, though it would take years and years for most users to get to even 1000 cycles.

Recycling. When your battery no longer holds a charge or its capacity is no longer useful, you can easily recycle it at over 30,000 locations in U.S. Canada such as Sears, Office Depot, Home Depot, Target, Wal-Mart, Best Buy, and others. Find the nearest location to you from Call2Recycle.

Memory Effect. While NiMH batteries supposedly don’t suffer from the memory effect that NiCd batteries supposedly did, NiMH batteries do sometimes suddenly deliver much reduced capacity each cycle. This can be easily fixed by a good charger that has a Refresh setting. (It drains the battery completely and then gives it a full charge, sometimes repeating the process a few times or until capacity no longer improves.)

NiZn (Nickel-Zinc).- A good rechargeable, better worse than NiMh in some ways

• Rechargeable
• Works great in high-drain devices
• Lasts longer in some high-drain devices than NiMH’s
• Higher voltage (1.65V) makes lights burn brighter (except some LED flashlights which regulate the voltage)

• The high voltage (1.65V) can burn out lights quicker, fry some electronics with no voltage regulator, and just not work in some electronics that do have voltage regulators
• High self-discharge rate (they lose ~13% of their initial charge per month just sitting around)
• Capacity plummets as the cells are cycled (used recharged)
• Requires a special, proprietary charger.
• Possible reliability problems (high failure rate: cells die quickly or self-discharge even faster than normal)
• They’re ever-so-slightly larger than normal, so they might not fit in those rare devices in which the batteries are already a tight fit.
• Semi-discontinued (see below; for now, Amazon has them, and the charger)
• Not available in any sizes besides AA and AAA

Reliability. PowerGenix NiZn’s suffer from reliability problems. See below for my poor experience with capacity. Also, NLee reports that after buying four cells and putting them through 20-30 deep cycles (0.9V), two failed (reduced voltage and Rapid self-discharging), and the other two suffer from reduced capacity (80% of original). Many customers on Amazon report their batteries dying prematurely too. It appears that over-discharging NiZn’s can easily damage them. (NiMH’s are more tolerant of an over-discharge.)

High-Drain Performance. High-drain devices are those which need lots of power quickly, like digital cameras. That’s as opposed to devices that just sip the juice slowly, like clocks. NiZn work great in high-drain devices, if the voltage isn’t an issue. (See the Voltage section below.)

Capacity and Run Time. There are many reports of reliability problems, including my own experience, which kind of make any published specs about capacity moot. I used 9 for about a year (probably fewer than 10 cycles) in electric toothbrushes and electronic door locks. Seven of the nine (Star Trek Voyager reference unintentional) dropped to only 45-150mAh in capacity, and the remaining two were 996 and 1298mAh. They should have been 2500mWh ÷ 1.65V = 1515mAh. NLee the Engineer says that after just a year, 2 of the 4 he purchased suffered reduced capacity down to 80% of the original, and the other 2 simply failed. Many others have made similar complaints. The following discussion assumes that NiZn’s don’t suffer reduced capacity early, although that’s probably not the case.

NiZn’s give either longer, shorter, or fairly equal run time vs. other kinds of batteries, depending on what device you use them in. engadget said that they got 300-400 flashes from their camera flash unit with NiZn’s, vs. only 200-300 with NiMH’s, and Tom’s Guide said their NiZn’s ran a CD player for three times longer than NiMH’s. However, devices which don’t limit the input voltage (like most flashlights and electric toothbrushes, for example) will run out faster with NiZn’s, because while the device was running the light was burning brighter or the motor was spinning faster. NiZn’s will make camera flashes recycle much faster, though burning through lots of flash shots quickly can fry the flash. Also, the NiZn might not give as many usable flashes as NiMH, since NiZn’s may start off with super-fast flash recycle times, but then get slower than NiMH. (Strobist quotes a user that said NiZn’s got worse than NiMH after 50-75 shots, and too slow to use after 200 shots, compared to 400 shots for NiMH.)

PowerGenix quoted capacity for AA and AAA was 1500 and 700 mAh respectively. That’s about half of the best NiMH’s. PowerGenix therefore listed the spec on its battery in mWh (total energy) rather than mAh, because total energy between battery types is more similar, and PowerGenix says that’s a more apples-to-apples comparison. That’s debatable, from either side. It’s true that the total energy is the same, but again, if the device being used doesn’t limit the voltage, the device will use the extra voltage and the NiZn will spend its energy faster, so the NiZn’s will provide less runtime. (And if the device does limit the voltage, then there’s no advantage to using NiZn’s in the first place, because the only reason you’d use them instead of NiMH’s is if you needed the extra voltage to begin with.)

Voltage. NiZn’s have the highest initial voltage of any rechargeable AA or AAA battery. The nominal voltage is 1.65, and fresh out of the charger the voltage is as high as 1.85V. (PowerGenix, PDF, and my tests) This is way higher than the 1.5V for alkalines. The higher voltage can be both a blessing and a curse. The upside is that flashlights burn brighter, and battery life will generally be longer in high-drain devices. (Some LED lights limit the voltage, so in that case NiZn’s won’t be brighter than 1.5 alkalines, but they’ll still be brighter than 1.2V NiMH’s.)

But there are downsides to the extra voltage. For lights, the brighter light means that the bulbs will burn out faster, sometimes immediately. ( Tom’s Guide) For cameras, a Rapid flash cycle can fry the flash. (Amazon review) For electronics, first understand that some devices have a voltage regulator (which limits the max voltage coming from the batteries) or a voltage protector (which shuts off the device if the battery input is too high). If your device doesn’t have one of these, and the device is very sensitive to voltage, then the batteries might fry it. It’s hard to know whether a particular device is a fry, auto shut-off, or no problem variety. (Good luck.) The fewer batteries your device takes, the less likely you are to have a problem. A one-batery device is the least dangerous, two-batteries are a little more so, four batteries even more, and with 8 batteries you’re just asking for trouble. Powergenix mostly ignores this problem in their marketing materials, so shame on them.

If you’re worried that NiZn’s could be too hot for your device, then NiMH would be a better bet. If NiMH doesn’t supply enough voltage for your device, you can mix NiMH and NiZn together, after seeing the caution about mixing NiMH and NiZn in the same device.

Self-Discharge. Powergenix claims a self-discharge rate of 8% per month, but NLee the Engineer’s tests showed 13% per month, and I’m inclined to trust him. Self-discharge means the bateries lose their charge by just sitting around, unused. Unlike NiMH’s, there is no low self-discharge version available. If you use up and recharge your batteries quickly this won’t matter to you. But if you need longer shelf life, you’ll want to consider a LSD NiMH instead.

Voltage Drop. Like most other rechargeables, NiZn batteries maintain most of their voltage over the whole charge and then suddenly plummet. This contrasts to alkalines, which lose their capacity steadily. For this reason many electronic devices that tell you how much battery life is left have a hard time reporting an accurate level for rechargeables, but this is especially true for NiZn’s, because their voltage is so high.

Charging. You need a special NiZn charger for these cells. NiMH chargers will not work! (See below for those who insist trying anyway.) PowerGenix made two chargers: the white charger was Smart and managed each cell separately, but had only one status LED and it didn’t light up until all the batteries were done. (If one cell was bad, the red charge light would blink. Then you got to play musical batteries figuring out which one was bad.) The black charger required charging in pairs, and didn’t manage the batteries separately. Never buy a charger like that.

The white charger is labeled a 1-hour charger, but what that really means is that the batteries mostly full after an hour, but not completely. Powergenix says it takes about 1.5 hours to charge 1-2 AA’s, and 2.5 hours to charge 3-4 AA’s.

Unlike NiMH’s, NiZn’s tolerate fast-charging well. The PowerGenix spec sheet suggests a rate of between C/2 to C is okay (30 minutes to 1 hour).

Charging NiZn’s in a NiMH charger. It’s theoretically possible to charge NiZn’s with a NiMH charger, but there are at least three problems. First, even a Smart NiMH charger probably won’t know when to stop charging NiZN’s, and will overcharge, damaging the battery. Overcharging is harder on NiZn’s than NiMHs. Second, how will you know when to stop charging? Armed with PowerGenix’s recharge profile chart (PDF) and the battery and charger specs you could make a guess. (Good luck.) Finally, the charging profile of a NiZn is different from a NiMH. A NiZN should get less and less charging current as it approaches fullness, but NiMH chargers don’t do that. The top-of-the-line La Crosse BC-series NiMH chargers put a minimum of 200mA into the batteries, for example, while the NiZn’s should get only about 100mA near the end of the charge. I don’t know the penalty for feeding more current than is recommended, but a shorter cycle life is my guess. Again here’s PowerGenix’s recharge profile chart (PDF). All that said, in a pinch, I’ve used my La Crosse BC-700 to slightly recharge NiZn’s while traveling when I forgot to pack my NiZn charger, but I’ve terminated the charge well before the cells could be overcharged. When you put the cells in the BC charger they’ll read FULL if their voltage is over ~1.3 volts, so I overrode that by pressing the cell button and then the Mode button to switch to charging mode. I monitored the voltage and took them out when they hit 1.8V, although you should be safe by going up to 1.9V. Even so, at that point your batteries will likely be only about half full. Anyway, all this is at your own risk, of course.

Discharged Voltage. The PowerGenix site provides absolutely no guidance as to how far NiZn’s should be drained before charging to maximize capacity and cycle life. (Shame on them.) The typical discharge level for rechargeable batteries is 1.0 to 1.1V, and 1.1V is when I try to recharge my batteries (both NiMH and NiZn). The charger won’t recognize them at

Problems with the charger. NLee says that the charger stops charging when the voltage hits 1.9V, but if the battery is damaged and can’t reach 1.9V, the charger will just keep charging and ruin the battery. That’s not my experience: I had a damaged cell that showed as full at only 1.16V.

NLee also says that batteries left in an unplugged charger will drain 10-100 times faster than batteries left in other chargers, which means that they’ll be discharged after only ten days.

Cycle Life. PowerGenix claims 100-500 cycles for their NiZn’s, compared to 100-800 for NiMH and NiCd, but they don’t specify the depth of discharge. NLee the Engineer says he found technical data on Powergenix’s site that says that their NiZn’s get only 200 deep-charge cycles, but I couldn’t find any such data (probably no longer there). NLee also reports that capacity suffered after only 12-16 deep cycles.

Recycling. NiZn’s are recycled in the same programs that take NiMH’s and NiCd’s. When your battery no longer holds a charge or its capacity is no longer useful, you can easily recycle it at over 30,000 locations in U.S. Canada such as Sears, Office Depot, Home Depot, Target, Wal-Mart, Best Buy, and others. Find the nearest location to you from Call2Recycle.

Li-ion (Lithium Ion) — not available in standard voltage, except for 9V

• Rechargeable
• Works great in high-drain devices

• The AA and AAA 1.5V sizes are more expensive, lower capacity, and less reliable than NiMH. The 9V size Li-Ion are good, though.
• Accidentally putting a 3.7V Li-ion in a 1.5V device could easily fry it.
• Requires a special charger

NiCd (Nickel-Cadmium) — low capacity and obsolete

• Rechargeable
• Work great in high-drain devices

• Pitiful capacity — lowest of any rechargeable battery
• Contain toxic cadmium. Can’t be disposed of in household trash. (Recycle it at over 30,000 locations in U.S. Canada such as Sears, Office Depot, Home Depot, Target, Wal-Mart, Best Buy, and others. Find the nearest location to you from Call2Recycle. If no recycling is available in your area, take your NiCds to your city or county’s hazardous waste facility.)
• Low voltage of 1.2V means that flashlights run dimmer, and devices needing 4 batteries might run through batteries quickly, or not work at all.
• High self-discharge rate (they lose 10% of their charge in the first 24 hours, and then 10% of their initial charge per month just sitting around)

Intro. NiCads are obsolete rechargeables. They’ve been replaced by Nickel-Metal Hydrides (NiMH). NiCd’s don’t have any advantages over NiMH, and they have lousy capacity and are toxic to boot. The only reason to use NiCd’s is if you already have some—though even then, if you upgrade to a modern battery you won’t have to charge them so often. NiCds are hard to find now, but why would you want to?

High-Drain Performance. NiCd’s deliver the juice fast enough to power high-drain devices like digital cameras—but not for long, since their capacity is so weak.

Capacity. Different brands have different capacities, but with NiCd it’s always low anyway (which is why you should be using NiMH instead). The AA size has 600-1000 mAh (compared to 1200-2900 for a NiMH), and the D size has 1800-5000mAh (vs. 2200-12,000 for NiMH). Note that many cheap chargers fill up the D size to only a AA capacity, giving really awful run time. (See our recomended chargers.)

Memory Effect. The theory of the NiCd memory effect is that if you repeatedly partially discharge a battery to the same level before charging it, it will remember the discharge level and then always fail at that point during use, never allowing the full capacity of the battery to be used. Many observers don’t believe that this effect is real, and most of those who do admit that it’s hard to reproduce and can be fixed by cycling with a good battery charger anyway. Now, NiCd’s (and NiMH’s) can suffer decreased capacity due to repeated deep-discharging or overcharging, and many people mistakenly blame the resulting reduced capacity on the memory effect. (Wikipedia, Dan’s Data, Repair FAQ) But the real problem wasn’t a memory effect, it was deep-discharging or overcharging. NiCd’s NiMH’s with reduced capacity can often be resurrected by exercising them (discharging down to 1.0V), or conditioning them in a charger that has a refresh mode. (Battery University, personal experience)

Self-Discharge. NiCd’s discharge quickly (meaning they lose charge just by sitting around, unused). They typically lose 10% of their initial charge in the first month, and then 10% of the initial charge each successive month.

Voltage. At 1.2V, no other battery has less voltage than NiCd’s. (For reference, alkalines are 1.5V.) This is generally not a problem, but it does mean that flashlights will be dimmer, and devices that need 4 or more batteries might not work at all.

Voltage Drop. Like most other rechargeables, NiCd batteries maintain most of their voltage over the whole charge and then suddenly plummet. This contrasts to alkalines, which lose their capacity steadily. (See the chart under NiMH.) For this reason many electronic devices that tell you how much battery life is left have a hard time reporting an accurate level for NiCd’s. The voltage is very similar for both a fully-charged battery and a nearly-spent battery.

Charging. Overcharging can reduce cycle life (the number of times the battery can be charged). Smart chargers know when the battery is full and stop charging. Dumb chargers run on a timer and will almost always overcharge or fail to fill up the battery completely, and they usually really fail to fill up C and D sizes. Note that even some Smart chargers are better than others. See the chargers page for charger recommendations.

You can charge whenever you like, but constantly draining them completely before charging shortens their life. Occasional draining down to 1.0V is okay, and recommended. Very slow charging can damage the batteries. (Ken Nishimura, an electrical engineer with a PhD from UC Berkeley)

Cycle Life. NiCd’s are good for hundreds of charge cycles in theory, but overcharging and repeatedly running the batteries down all the way can reduce cycle life. To avoid overcharging, use a Smart charger that stops charging when the battery’s had enough. (See the chargers page for recommendations.) You’ll also get more cycles if you charge your batteries before they’re fully run down.

Recycling. When your battery no longer holds a charge or its capacity is no longer useful, you can easily recycle it at over 30,000 locations in U.S. Canada such as Sears, Office Depot, Home Depot, Target, Wal-Mart, Best Buy, and others. Find the nearest location to you from Call2Recycle.

9V size is especially puny. NiCds are already very weak compared to NiMH, but the 9V size of NiCds is especially weak. NiCd 9V voltage is actually only 7.2V (or 8.4V if you’re lucky), while NiMH voltage is typically 9.6V or sometimes 8.4V. See more on 9V-size rechargeable batteries.

Rechargeable Alkalines (RAM).- higher voltage long shelf life

• Rechargeable
• Slow discharge rate (long shelf life)

• Short cycle life (can’t be charged as many times as a real rechargeable like NiMH or NiZn)
• Tiny initial capacity in some brands
• Capacity (and sometimes voltage) is reduced on every cycle
• Doesn’t work in high-drain devices
• Requires a special charger, and charges much slower
• Way more prone to leaking than any other kind of battery

Summary. These are often called RAMs, for Rechargeable Alkaline Manganese. When they came out in 1992 they were competing against rechargeable NiCd’s, and claimed the best of both worlds—reusable like a NiCd, but with the higher voltage and long shelf life of an alkaline. Those advantages have been narrowed now that LSD NiMH’s offer long shelf life and NiZN’s offer higher voltage, but RAMs remain the only battery that offers both long shelf life and higher voltage in the same package. Of course, there are some downsides:

• RAMs can be deeply-discharged and then recharged only 5-100 times, vs. many 100’s of times for NiMH or NiZN.
• The battery capacity is reduced significantly on every cycle. Ouch!
• In some brands, the voltage is reduced on every cycle too. There goes one of the whole reasons for using RAM vs. NiMH in the first place.
• RAMs don’t work well in high-drain devices like digital cameras. (But they’re great in things like clocks, flashlights, and remote controls.)
• RAMs, like regular alkalines, are prone to leaking (unlike real rechargeables like NiMH and NiZn which are virtually leak-proof).

Where to Buy. There were only a couple of manufacturers left circa 2012, and now that I check again in 2017, it appears there are no more sources. (As for the 2012 manufacturers, Pure Energy seems to have gone out of business, and Accucell doesn’t make RAMs any more. Rayovac discontinued its Renewal brand RAMs in 2004, and the Juice and Lenmar brands appear to have disappeared circa 2011.)

High-Drain Performance. RAMs don’t work in devices that need lots of juice quickly, like digital cameras. For high-drain devices use NiMH or NiZn.

Capacity. Initial capacity of RAMs is often dramatically lower than a real alkaline, or even a NiMH for that matter. Also, the capacity of a RAM decreases after every use/recharge cycle. For example, Pure Energy brand RAMs lose half their capacity after 25 deep-discharge cycles. ( PDF) Lenmar are worse, becoming useless after 25 deep-discharge cycles. Considering that the capacity drops on each recharge cycle, a Lenmar RAM effectively provides the same amount of energy over 25 cycles as 10 regular alkaline batteries would have. In other words, a single Lenmar RAM replaces a whopping 2.5 regular alkalines, and then only after you’ve screwed around recharging it 25 times.

RAMs retain much more capacity and can be recharged many more times if they’re recharged before being depleted—the sooner the better. They may be able to be charged 100’s of times that way, and will offer much more lifetime capacity vs. deep discharging. Of course, it’s a hassle to constantly recharge your batteries when they’re only partially drained.

Self-Discharge. RAMs have the lowest self-discharge rate of any rechargeable battery—less than 1% of their initial charge per month. That’s way less than even the low self-discharge flavor of NiMH’s. This makes RAMs good for infrequently-used devices, or devices which take months to use up the battery (e.g., clocks). Though I’d still prefer LSD NiMHs, and avoid the risk of leaks.

Voltage. At 1.5V, the RAMs voltage is just about ideal compared to other rechargeables—it’s higher than the 1.2V of NiMH’s (so lights run brighter), but lower than the 1.65V of NiZn’s (so you don’t risk blowing bulbs or frying electronics). However, just like the capacity drops on every charge, voltage can drop as well.

Charging. You need a special charger for RAMs, a regular NiMH charger won’t work. Capacity is retained (and cycle life is greatly increased) by charging RAMs before they’re fully depleted—the sooner the better. RAMs will offer much more lifetime capacity this way. RAMs take a lot more time to charge than other rechargeable batteries. Here’s my page of RAM chargers.

Cycle Life. RAMs offer the fewest deep recharge cycles of any rechargeable battery, but if you’re not charging your batteries every day RAMs could be a good fit for you. (If you are charging your batteries every day, look at NiMH or NiZn.) The worst RAMs likely get at least 20 cycles. Pure Energy claims at least 50 deep recharge cycles, thanks to a combination of improved battery chemistry and their optimized battery charger. For shallow discharges, recharge cycles could go into the hundreds, and at least in Pure Energy’s case, into the thousands. (See Pure Energy’s PDF report.)

Recycling. It’s a lot harder to find places to recycle RAMs than real rechargeables like NiMH and NiZN. See the Alkalines Recycling section for more.

Why there aren’t 9V rechargeable alkalines. From the Rayovac website: There are two reasons: (1) 9V batteries actually have six small 1.5 V-cells inside them. Reusable alkalines need to be charged individually for reliable performance. Since you can’t access each cell inside the 9V battery individually, they could not be reliably recharged. (2) Most products designed to run from 9-Volt batteries last for many months. Recharging these batteries provides limited benefit in terms of cost savings (the cost of replacing batteries is not significant anyway).

Battery University on rechargeable alkalines.

Step-by-step guide for first-time homebuyers.

What is the Voltage of a AAA Battery? (Averages Types)

Ever wondered how much power a tiny AAA battery packs? Well, you’re in luck because, in this article, we will dive into the world of AAA batteries and explore their voltage.

The average voltage of a non-rechargeable AAA battery, like alkaline and zinc-carbon, ranges from 1.5V to 1.8V. Rechargeable batteries, on the other hand, typically have a 1.2V voltage.

These little powerhouses might not seem like much, but they keep our portable devices running smoothly.

I will go into more detail below.

The Voltage of AAA Batteries

AAA batteries are like the smaller siblings of AA batteries but just as vital for powering our everyday gadgets, right? So let me share some cool facts about the voltage of these handy little powerhouses.

First off, the ideal voltage for an AAA battery is 1.5 volts. Surprisingly, when fresh out of the package, they read between 1.35 and 1.45 volts.

I had a lightbulb moment when I discovered this slight variation! That’s still enough juice to keep our devices up and running.

Now, not all AAA batteries are created equal. There are generally two types: rechargeable and non-rechargeable.

The non-rechargeable ones are often alkaline or zinc-carbon batteries, while the rechargeable ones are usually NiCad or NiMh.

The non-rechargeable ones have a voltage of 1.5 volts, while the rechargeable ones have a slightly lower voltage of 1.25 volts.

Want to check the voltage of your AAA batteries at home? Here’s a nifty trick! You can use a voltmeter to do so. Just set it to the “20” DCV setting and test away.

That’s what I do when I’m feeling like a battery-testing superhero!

Types of AAA Batteries and Their Voltages

Non-Rechargeable AAA Batteries

Non-rechargeable AAA batteries are always there when you need them. Their most common type is the alkaline battery. These little powerhouses have a nominal voltage of 1.5 volts.

When we talk about zinc-carbon batteries, we also find a 1.5-volt output, but they often have a shorter lifespan.

Then there’s a more exotic type called lithium iron disulfide (Li-FeS2) batteries. These high-performance batteries also give you 1.5 volts up to a peak of 1.7V.

However, they can up the ante in extreme conditions like freezing temperatures or high-drain devices.

Rechargeable AAA Batteries

Now, let’s move on to rechargeable AAA batteries. You may call them the eco-friendly alternative, and you’d be right!

They’re perfect for those devices you use daily and you don’t want to buy new batteries.

Nickel-metal hydride (NiMH) is a popular choice for rechargeable batteries. These bad boys offer a slightly lower 1.2-volt output but can be recharged hundreds of times.

Depending on the brand and quality, they are available in various capacities, usually 600 to 1100 milliamp-hours (mAh).

Nickel-Cadmium (NiCad) batteries have a nominal voltage of 1.2 volts and are known for their durability and ability to handle high loads.

However, they also have a relatively low energy density and can suffer from a “memory effect” if not properly maintained.

Factors Affecting AAA Battery Voltage

Manufacturing Tolerances

Regarding AAA batteries, it’s important to consider manufacturing tolerances. These little guys can have slight variations in voltage right out of the package.

I’ve found that a fresh AAA battery should measure between 1.5 and 1.7 volts with a digital voltmeter.

Just don’t sweat the small stuff – a tiny difference in voltage shouldn’t impact your device’s performance too much.

Temperature Effects

Now let’s talk about temperature. I’ve been out in the sun building houses, and trust me; the temperature can affect everything! The same goes for AAA battery voltage.

When a battery gets hot or cold, its voltage may change slightly. So, whether chilling in the snow or sweating in the sun, be aware that temperature could affect your batteries.

State of Charge

Finally, let’s chat about the state of charge for a moment. As your AAA battery loses its charge, you’ll notice its voltage dropping too.

A brand new AAA battery has a voltage of around 1.5 volts, but as it loses its energy, it will go down to around 1.2 volts. And when it’s completely out of juice? You’ll see a voltage of about 0.9 volts.

So, there you have it, folks! That’s the scoop on the factors affecting AAA battery voltage. Stay charged, and keep powering through!

Wrapping Up

AAA batteries come in different types like Zinc-carbon, Alkaline, and Li-FeS2. Each type has its voltage, but typically, AAA batteries have voltages of 1.5V.

A AAA battery can reach up to 1.7V, while a dead one might fall to around 0.9V.

Next time you’re looking for AAA batteries, remember to check the voltage (usually indicated on the battery itself) and ensure it’s compatible with your device.

Remember that non-rechargeable AAA batteries typically have voltages ranging from 1.5V to 1.8V. Now you’re all set to power up your favorite devices without worry!

• “Batteries in a Portable World: A Handbook on Rechargeable Batteries for Non-Engineers” by Isidor Buchmann
• “The Battery: How Portable Power Sparked a Technological Revolution” by Henry Schlesinger

Video References

Hello, I’m Sam. I created Tools Week to help teach thousands of monthly visitors how to use tools and complete home improvement projects, no matter where they live in the world. about us.