# Battery Tips. Aaa battery watt hours

## Understanding battery capacity: Ah is not A

I used battery holders for eight “C” alkaline cells on my robot after not finding a 12V, 1A battery.

My earliest electronics projects and my first robot were powered by regular alkaline batteries, and I didn’t think about current or the capacity of those batteries. The batteries were prominently labeled “1.5V”, and I was happy in my understanding that putting four in a battery holder got me to 6 volts; when the motors slowed down, it was time for new batteries. When I began designing my second robot, I found some 12V, 1A motors (what a “1-amp motor” might mean is a topic for another post) and promptly wasted many hours dragging parents and teachers to Radio Shack and car parts stores looking for a 12V, 1A battery. No one understood that the batteries were labeled with capacity, not current, and since the smallest 12V motorcycle and alarm system batteries in town were 3Ah or 4Ah, I went home empty handed. I ended up using alkalines. Apparently, once the battery capacity wasn’t in my face, I forgot about my concern that they would force too much current into my motors.

• Not understanding that my circuit would draw whatever current it wanted from the battery, as opposed to the battery forcing a given amount of current into the circuit.
• Thinking that my motors would draw a fixed amount of current.
• Confusing current and capacity.
• Ignoring the “h” in “Ah”
• Forgetting about a property, such as capacity, as soon as it wasn’t in my face.

The first two points are complex enough that further elaboration would merit their own posts; today I want to FOCUS on some technical details of battery capacity and current and touch on the sloppy attitude that leads to the last two mistakes.

A battery stores energy; the “capacity” is how much energy it can store. Energy is measured in joules, abbreviated J, but it can also be expressed in different units such as watt-hours, abbreviated Wh (for larger quantities, such as residential electricity use, kilowatt-hours (kWh) are used; a kWh is a thousand Wh). This is similar to the way area can be measured in acres or in square miles: there are units specifically for area, such as acres, but you can also arrive at a measure of area by multiplying length by length, to get mile-miles, or the less awkward square miles. (The hyphenation imposed by English grammar does not help matters since the hyphen looks like a minus sign when we are actually multiplying the units together.) Watts and watthours are generally good units for electronics since they are easily related to voltage and current and since typical batteries that you can hold in your hand will have a capacity of a few dozen watt-hours.

In the case of a typical battery, where we can assume a constant voltage, we can replace watts with volts multiplied by amps. A 12-volt, 1 amp-hour (abbreviated Ah) battery and a 6-volt, 2Ah battery each store 12Wh, but the voltage is usually a critical parameter for a battery, and once a voltage is selected, the capacity can be specified by the amp-hour rating. The value in using the amp-hour is that it makes explicit our multiplication of rate, the amp, and time, the hour: a battery rated for one amp-hour can provide a current of one amp for about one hour, two amps for about half an hour, or 0.1 amps for about ten hours. I say “about” because the exact capacity will depend on the current.

The current and capacity for a battery are like the speed and range of a car. If your car has a range of about 300 miles, you can go 30 miles an hour for ten hours, or 60 miles an hour for five hours. Your efficiency will get worse with speed, so by the time you go 60 miles per hour, you might run out of gas after only four hours, for a range of 240 miles. Going back to my battery search, looking for a 1-amp battery was like looking for a car with a speed of 60 miles: 60 miles isn’t even a speed, and even if I revised my search to a car that could go 60 miles per hour, it still wouldn’t be a useful specification to look for. Most batteries on the scale I was looking at can deliver one amp, just like most cars can go sixty miles per hour. The maximum available current, like the maximum speed of the car, might be a more reasonable specification to search for, though providing those kinds of specifications might make the respective manufacturers nervous.

It is reasonable, though, to consider the maximum current a battery can safely deliver. That value will depend on all kinds of things, including the chemistry of the battery, but the maximum discharge rate is almost always tied to the capacity. That means that given a particular technology, a battery with double the capacity can deliver double the maximum current. Batteries are often specified with a discharge rate in terms of C, where C is the capacity of the battery divided by hours. For example, for a 2Ah battery, C is 2A. If the battery has a maximum discharge rate of 10C, the maximum current is 20 amps. It’s good to keep in mind that a 10C discharge rate means a battery life of less than 1/10th of an hour, and with the loss of capacity that a high discharge rate generally causes, the battery life would be less than five minutes.

As I tried earlier to recall what happened with my failed battery search, I was struck by the extent to which I ignored the “h” in the “Ah” specification and the ease with which I forgot about my critical “1-amp battery” requirement when I returned to the alkaline batteries. Unfortunately, this kind of carelessness or sloppiness is common, especially for beginners who might already be overwhelmed by all the information they need to sort through and who have not yet had the experience of losing time and destroying hardware because of inattention to details. I do not have any particular solution to this problem beyond reminding you to pay attention and think about how things should work before just hooking things up. Be on the lookout for contradictions; seeing “Ah” where you expect “A” should definitely make you very uneasy and lead you to reevaluate your expectations.

• A typical alkaline or NiMH battery in the standard “AA” size has about 2000 to 3000 mAh (or 2 to 3 Ah). With a cell voltage of 1.2 V to 1.5V, this corresponds to 2 to 4 Wh per cell. When multiple cells are used in series, as with the use of a battery holder or most pre-made battery packs, the voltage goes up but the capacity in amp-hours stays the same: an 8-cell NiMH pack made of AA cells will have a 9.6 V nominal voltage and a 2500 mAh capacity. There can be quite a range in capacities depending on the quality of the batteries. For larger cells, such as C and D size, the capacity should go up approximately proportionally to volume, but some cheap units (they’re usually light) can have the same capacity as the smaller cells. Alkaline cells have a more pronounced drop in capacity as the current drawn out of them goes up, so for applications requiring several hundred mA or more current, NiMH cells of the same size could last significantly longer. For low-current applications that need to run for months, alkaline batteries can last much longer because NiMH cells can self-discharge in a few months.
• 9V alkaline batteries can be convenient for their high voltage in a small size, but the energy density (watthours per given volume or weight) is the same as other batteries with the same chemistry, which means the capacity in amp-hours is low. In approximately the same size as an AA cell, you get six times the voltage, so you also get about six times less in the Ah rating, or about 500 mAh. Given the high losses incurred from discharging in anything under a few hours, 9V batteries are impractical for most motors and therefore for most robots.

Coin or button cell batteries.

• Coin or button cell batteries vary in size and chemistry, but you can generally expect 1.5 to 3 volts with a few dozen to a few hundred mAh.

• Lead-acid batteries are popular for larger projects since they are usually the lowest-cost option and are widely available. Sealed lead-acid or gel-cell batteries are available in 6 V and 12 V versions (other multiples of 2 can be found), with the 12 V versions weighing about a pound per amp-hour. 12 V car batteries store a few dozen amp hours, and they weigh a few dozen pounds.

11.1V, 1800mAh Li-Po battery.

• Lithium-based rechargeable batteries have around double the energy density of alkaline and NiMH batteries by volume and even better improvements by weight. These newer batteries are far less standardized in terms of battery size and shape, but since they are usually intended for applications where capacity or maximum battery life are important, these batteries usually have their voltages and capacities prominently labeled.

### Introduction to Jan’s blog

by Jan. 12 November 2010 My name is Jan Malášek, which is a Czech name, so the “J” is pronounced as an English “Y” (if you care, we can go over the last name in person, or.

by Jan. 19 November 2010 How many volts of current are there in a bolt of lightning? That’s the kind of stupid question your local news anchor might ask while bantering.

## 2 Комментарии и мнения владельцев

Thanks for the article Jan!

It’s probably worth noting, particularly for lead-acid batteries, that the capacity is usually listed assuming that the battery will be discharged over a 20 hour period. If you’re using it in relatively high current applications (i.e. robotics or motors of any kind) then you can expect almost half of that. This is something that caught me out when I was looking at battery options.

Great comment; I’m sad that I neglected to mention that. Another variable to consider is how far the battery is allowed to discharge before being considered fully drained.

## Battery Tips!

See the home page for which kind of battery is best, and which brand of battery is best. For NiMH specifically, see my comparison of NiMH brands.

### You can mix brands together

The manufacturers tell you that you should use only the same brand batteries together, but they don’t provide any good justification for that. Whether alkalines or rechargeable, voltage is voltage, and your device neither knows nor cares who made the batteries. Your device is certainly not going to tattle on you to the manufacturers. Now, if your alkalines had very different capacities then that could promote leaking, but the difference between most alkalines isn’t that great, and you shouldn’t really be using alkalines for most purposes anyway. For rechargeable batteries, again, just try to match the capacities as close as possible, not to prevent leaking (since rechargeables almost never leak), but to avoid reducing the cycle life of the lower-capacity battery.

## Costs

### How much money do I save with rechargeable batteries instead of alkaline?

For a device that goes through a set of four AA’s every 15 days (e.g., use the device 1 hour a day and a set gives 15 hours of runtime), switching to rechargeables saves about 100 a year. And yes, that includes the cost of recharging the batteries, which is negligible. The alkalines cost around 99 a year, vs. only 31¢/year in electricity to charge the NiMH batteries, after a first-year cost of 25 for a charger and a set of batteries. (Showing the ret of my work: 365 days a year ÷ 15 days/set = 24.3 sets/year, x 3.78(8% tax) = 99 for the alkalines. Charging cost is figured as: 20 wH to charge a single AA, x4 in a set, x 24.3 sets a year, x 16¢ per kWh.)

### How much does it cost to charge a NiMH AA battery?

In electrical costs, less than a penny. Charging it three times would cost about a penny. This assumes an electrical rate of 16¢/kWh.

## Voltage

### Possible voltage problem with NiMH batteries

• 1 battery. The 0.3V difference between 1.5V and 1.2V is rarely a problem.
• 2 batteries. Now the device expects 3.0V from alkalines but you give it only 2.4V from NiMH. The 0.6V is more likely to be a problem than it would be in a 1-battery device, but you’re still probably fine.
• 3 batteries. Now the differences are much more likely to manifest. I have lots of headband flashlights, and they’re noticably dimmer and give less runtime with the 3.6V provided by the NiMH vs. the 4.5V that they’re expecting from alkalines. Unfortunately there are few headlamps designed with NiMHs in mind, but both the Zebralight and the Fenix HL21 take a single AA and are super-bright. I have one of each, and I love them. (Here’s a comparison of the various Zebralight models.)
• 4 batteries. Now we’re looking at a 6.0. 4.8V = 1.2V difference. That’s pretty sizable, and I’m not surprised by poorer performance at this point.
• 6-8 batteries. You will almost certainly have problems here. Giving 9.6V when the device is expecting 12V is just asking for poor performance.

If you’re not careful about mixing NiZn and NiMH together, you can easily kill your NiZn’s. Your NiZn’s will usually run out faster when you mix them with NiMH’s, and if you don’t stop and charge the NiZn’s soon enough, the NiZn’s will be damaged or dead. The solution here is to either make sure that all the mixed batteries have a similar mAh capacity (not mWh), or else be really diligent about monitoring the voltage of your NiZn’s, charging them well before they get down to 0.5V (preferably charging when they drop to around 1.0-1.1V). As to the former (matching mAh capacity), that means you’ll have to find and use lower-capacity NiMH’s, because most NiMH’s have a larger mAh capacity than NiZn’s.

You might think you have to match only mWh and not mAh, because mWh is the total energy. That would be convenient, because mWh for common NiZn’s and NiMH’s is similar. But you really do have to match mAh, not mWh. The reason is that in devices which don’t limit the voltage to about 1.2V, they’ll make use of the NiZns’ extra voltage. For example, the light will burn brighter, or the toothbrush will spin faster. So even if the total energy expended between both kinds of batteries is the same, the NiZn expends it faster, because it’s running at a higher rate. Another way to look at it is that, as NLee points out, the same amount of current (amps) flows through both batteries, regardless of what the voltage is. So if the device is drawing 350 mA (or whatever) from each battery, then the device with the fewer mAh is going to run out faster. That’s usually going to be the NiZn.

Another solution to the problem of insufficient voltage from NiMH batteries is to make a power pack. If your device has an input for an AC/DC adapter, you can get battery holders from Radio Shack for just a few bucks, and wire them together (red wire to black wire), then attach a power plug so you can plug it into your device. If that doesn’t make sense, just go into Radio Shack with your device, tell them you want to make a battery pack with battery holders for it, and ask them what you need. Be sure to tell them you’ll be using 1.2V NiMH batteries and that you want to use an extra battery or two to get the right voltage. For example, if your device expects 6V and takes 4 batteries, then you’d actually use five batteries, because 5 x 1.2V = 6.0V.

### Milking every last drop out of your alkalines

For most purposes you should be using NiMH instead of alkalines, but if you have some alkalines for whatever reason, these tips will help you get all the energy available from them.

Different devices stop working at different low voltage levels (the cutoff voltage). It could be 1.3V in a halogen flashlight, but only 1.0V in a clock or 0.8V in a radio or remote control. The tip here is that if your alkaline has died in a high-demand device like a flashlight, it could have a second life in a lower-demand device like a remote control or a clock. (Popular Mechanics has a table of cutoff voltages.)

Also, you can make a battery pack with a battery holder from Radio Shack or Amazon to milk your alkalines completely. For example, I have some battery-powered Christmas lights that expect 4.5V (three 1.5V AA’s). I have some alkaline AA’s that are around 1.15V. (I don’t buy alkalines, I salvaged these from elsewhere.) Three of them would be only 3 x 1.15V = 3.45V, which would be kind of weak for the lights. But putting four of them in a battery pack gives me 4 x 1.15V = 4.6V, which is just about perfect.

Alkaline voltage drops sharply after hitting 0.9V, so consider a 0.9V alkaline as completely dead and useless.

## Battery Leaks

Since it’s really only alkaline batteries that leak, see my section on alkaline batteries for info about leaking.

## Batteries in sets don’t all die at the same time

When the batteries in your device go dead, there’s a good chance that only one is really dead. The rest likely still have some juice in them. How can you use this info? Depends on the battery type:

For rechargeable batteries (e.g., NiMH or NiZn): If one battery discharged early, it’s limiting your total runtime. The bad battery is the weak link in the chain. Test the voltage of all the batteries and if one or more is above ~1.17V while others are closer to 1.10V, refresh the dead cell(s) in a Smart charger.

## What is a dead battery?

Unfortunately, it’s common to use the single word dead to refer to two different conditions: One, a battery that has been discharged (used all its capacity), and two, a rechargeable battery that can’t be recharged any more. Dead is a poor word for a NiMH that’s simply empty, because if you can bring it back to life, then it’s not really dead. A better term for a discharged NiMH might be sleepy. Though on this site, I try to use discharged to refer to a battery whose capacity has been drained, and dead to refer to a battery which can’t be resurrected.

## When is a battery dead / discharged?

NiMH, NiZn, NiCd. Charge them before they hit 1.0V. You could wait until they hit 0.9V, but you’ll get more cycle life if you recharge them sooner.

See below for how to test battery voltage.

## How to tell how much energy is left in a battery

Alkalines. Alkalines start at 1.5V and lose voltage at a pretty steady rate until about 1.0V, at which point the voltage plummets. So if you tested an alkaline and it was halfway between 1.0V and 1.5V (i.e., 1.25V), it would be about half drained.

See below for how to test battery voltage.

## How to test battery voltage

Battery testers are fine. But multimeters connected directly to an unloaded battery often give inaccurate readings. Unloaded means not actually powering something, and unloaded voltage is often higher than the loaded voltage. Battery testers supply a small load. Multitesters do not. To test voltage with a multitester, stick the battery in the device, turn it on, and then test the voltage.

An unloaded 9V might test as 10V unloaded but only 5.6V with a small load applied. (sounce, PDF, p. 9) That doesn’t mean that every battery that tests as 10V unloaded will test as 5.6V under load; most batteries will usually test just a little lower under load, but some will test a lot lower. Every battery is different, so that’s why you can’t trust the reading unless you test under load.

## Understanding electrical terms

Volts (V). Voltage is a measure of how hard the electricity comes out. It’s electrical pressure. So in devices with motors, applying a higher voltage will make the motor spin faster. A device doesn’t choose the voltage it wants, it just receives whatever voltage is supplied by the battery. That is, it’s the battery that decides the voltage. See Voltage above for how this relates to AA and AAA batteries.

Amps (A). Amps are a measure of current, which means how many electrons are flowing. A device will try to draw as many amps as it needs from the battery. That is, it’s the device that decides the amp rate, not the battery. (Note that this is the opposite of voltage.) A high-drain device is one that needs lots of amps quickly. Regular alkaline batteries are terrible for those devices because they can’t pump out the amps fast enough, but NiMH are great.

Amp-hours (Ah). This is a measure of how many amps are stored in a battery. That is, it’s a measure of the capacity of the battery. A battery with more amp-hours has a higher capacity and will give more runtime before being depleted. A battery with more amp-hours does not make a motor spin any faster. Because batteries are small, we measure their capacity in milliamp-hours (mAh).

Watts. Watts is a measure of power, and is a combination of volts and amps. Actually its volts times amps. When you take how hard the electricity is pumping (volts) combined with how many electrons are flowing (amps), then you’ve got your total power. Think about it: If you hit me with a paper plane going 30mph it’s not going to hurt me very much. That’s like high pressure (the 30 mph speed) but low flow (since you’re not throwing much matter), so the pressure x flow isn’t very much. Similarly, if you slide a refrigerator into me at 0.1 mph it’s not going to hurt me very much. That’s low pressure (the 0.1 mph) with high flow (a huge refrigerator, lots of matter), so again the total power isn’t very much. But if you hit me with a refrigerator going 30 mph, then suddenly you can see how that’s a lot of power.

Watt-hours. We just saw that watts is a measure of the rate of power at any given instant. The amount of energy consumed is measured in watt-hours. (Or in the case of batteries, milliwatt-hours, since batteries are small.) Say you’ve got a 1.2V battery and a device that draws 150 mA. The rate of power is 1.2V x 150mA = 180 mW (milliwatts). Now let’s look at the battery. Your battery is rated as 2000 mA. So your battery has 1.2V x 2000mAh = 2400 mWh. Your 2400 mWh battery divided by the 180 mW draw from your device means you could run your device for about 2400 mWh ÷ 180 mW = 13.3 hours.

## What do I do if I swallow a battery?

Call the National Battery Ingestion Hotline immediately at 1-202-625-3333 (open 24 hours, and can call collect if necessary). You can also call your local poison center at 1-800-222-1222. (Calls are automatically routed to the poison center for your area.)

## Why you don’t get shocked

As you may have guessed, there’s just not enough power in household batteries to do you any harm. It’s the exact same kind of electricity that can kill you, but there’s just not nearly enough of it. Batteries put out juice when something comes between the positive and negative ends of the battery. When you come between the two ends by touching them, your body provides resistance to the tiny 1.5 V in a household battery, so the current can’t flow from one end of the battery to the other, and no real circuit is formed. When that battery is in your appliance, however, the metal parts readily accept the current, and the juice flows out one end of the battery, through the device where most of it’s used up, and then the remaining current goes back into the other end of the battery. Once I had a 9V battery and a wire dish scrubber in my (Don’t ask me why.) After a few hours the items shifted and the scrubber was touching both terminals of the battery. I noticed something hot in my. getting hotter, almost painfully hot, before I realized what it was. If I didn’t take them out of my and separate them then I tend to think I would have burned a hole in my pants. So don’t put batteries in the same as keys or coinsespecially 9V batteries.

## AA, AAA, C, and D are really cells, not batteries

In technical terms, a cell is a single energy-producing unit, while a battery is multiple cells strung together. So AA’s aren’t really batteries, they’re actually cells. A 9V is truly a battery, because it contains 6, 7, or 8 individual cells. (That’s what you’d see if you unwrapped it.)

Is this important? Of course not. The general public uses the word battery instead of cell, there’s no way to stop them, and even if we could there would be absolutely no benefit in doing so. So I use the familiar term battery instead of cell throughout this site, because that’s what people are familiar with. I put this section here to let the nitpickers know that I do understand the difference, and to point them to it when they email me to complain. (Yes, some people really don’t have anything better to do.)

## Can You Take Batteries On A Plane?

Flying with batteries on a plane is possible in most circumstances. The rules around them can be irritating but they are in place for flight safety so we can’t complain too much.

You need to identify what kind of battery you are taking because not all batteries are treated equally.

Any batteries you take with you on planes should be for personal use. Don’t go trying to buy a bunch of batteries on vacation that you think you can sell back home for more!

The short answer is, yes you can bring most batteries on planes, but spare lithium batteries and large lithium batteries like battery packs deserve special attention. It’s worth reading this post to understand the nuances about traveling with batteries.

The full post will only take a few minutes to read and you’ll soon be an expert on batteries in luggage.

Let’s power-through and get you trained up!

## TSA Battery Rules

The Federal Aviation Administration (FAA) sets the rules about what batteries are allowed on planes.

And it’s the job of the Transportation Security Administration (TSA) to enforce those rules and make sure no prohibited batteries make it into either carry-on baggage or checked baggage.

The following chart summarizes what kinds of batteries the TSA allow you to take on planes:

Kind Of BatteryCarry-on In DeviceCarry-on SpareChecked In DeviceChecked Spare
Dry Alkaline Batteries (AA, AAA, C, D) Yes Yes but protect from damage and short circuit Yes Yes but protect from damage and short circuit
Dry Rechargeable NiMH NiCAD (AA, AAA, C, D) Yes Yes but protect from damage and short circuit Yes Yes but protect from damage and short circuit
Lithium Ion Under 100 watt hours Yes Yes but protect from damage and short circuit Yes No
Lithium-ion 101 – 160 watt hours Yes, but airline approval required. Yes, but airlines approval required and protect from damage and short circuit No No
Lithium Metal Under 2 grams lithium per battery (AA, AAA, coin-like batteries for watches etc) Yes Yes but protect from damage and short circuit Yes No
Nonspillable wet batteries Yes Yes but protect from damage and short circuit Yes Yes but protect from damage and short circuit

### Lithium Ion Batteries Under 100 Watt Hours

Lithium batteries power many of our modern electronic devices like cameras, laptops, tablets, cell phones, kindles, or portable vacuum cleaners.

That’s why spare and loose batteries should always be packed well to avoid any impact damage if your suitcase is thrown around.

It’s also a good idea to put some tape over the terminals to stop any chance of the battery catching fire.

## FAQ’s

A spare lithium ion battery that is not installed in a device will not be permitted in checked luggage. The TSA will scan your suitcase and remove this if they discover it.

Batteries install in devices are allowed in checked luggage. It’s only spare batteries or power packs that are not allowed in checked luggage. The reason for this is that there is risk that a metal object such as a coin could connect the positive and negative ends of the battery causing a short. If this was to happen inside the hold luggage there is a risk that the battery could go on fire and in the hold luggage there is nobody around to extinguish a fire.

Batteries with a capacity larger than 300 watt hours are never allowed on airplanes.

Yes alkaline batteries are allowed in checked luggage. As always make sure they are well packed and can’t be damaged should your case be thrown around. Also, make sure they are not packed alongside metal objects that could cause a short circuit.

Battery packs are allowed in carry on luggage only. You cannot pack a power bank or power charger in checked luggage.

Lithium-ion batteries are a type of rechargeable battery. They can store large amounts of energy in a small form. This is great for powering your laptop for hours but on planes this means they are a fire risk. If anything goes wrong with a lithium-ion battery they can release a lot of energy.

You can take lithium-ion batteries on planes in your carry-on luggage. That way should there be any fire someone will be around to put it out.

You can take as many lithium batteries as you need in carry on luggage provided they are under 100 watt hours.

Lithium batteries have a higher energy density and this makes them a risk. They are allowed on planes in carry on luggage in smaller sizes.

Yes you can bring regular alkaline AA batteries on an airplane in either carry-on or checked bags. You can also bring rechargeable AA NiMH or NiCad batteries. The only AA battery that you can’t pack in checked luggage is a long life AA lithium metal battery.

Yes you can bring alkaline AAA batteries on planes in checked or hand luggage.

You can bring portable phone chargers or portable laptop chargers on planes but they must be packed in carry on luggage. If your power pack is under 100 wh you are good to go. If your power pack is between 101 and 300 wh you need to seek permission from your airline. If your power pack is over 300 wh you are unable to pack it anywhere.

Yes camera batteries are allowed on planes. Spare batteries should be packed in carry on. Cameras with batteries installed can be packed in checked luggage. However, a camera is exactly the type of thing that gets stolen from checked luggage so be sensible and pack it in your hand luggage.

## The Verdict

Most batteries are permitted in carry on and checked luggage.

The big exception is spare (uninstalled) lithium metal and lithium-ion batteries which are only allowed in carry on bags.

Exceptionally large batteries might need airline permission. You’ll probably know if you have an extra large capacity battery.

Always protect all batteries when you pack them. If they are installed in the device that usually gives protection from damage or short circuit.

If they are spare and uninstalled you need to think a little more. A packing cube could be a good way make sure a spare battery is protected and isolated from any metal that could cause a connection between the positive and negative terminals.

Make sure that any battery-powered device is powered off and can’t be accidentally activated by items pressing against a power button.

That’s it. You are now an expert in flying with batteries, packing them, and taking them on airplanes.

## Introduction: How to Check AA/AAA Alkaline Battery Using a Voltmeter

We all run into a situation when batteries in our remotes, toys, keyboards/mice run out. If we don’t know how to check a battery we might throw out a perfectly fine battery (especially when we have a pile of them somewhere in the drawer).

This electronics tip has to deal with checking common alkaline AA/AAA batteries or AA/AAA rechargeable batteries for proper voltage with a voltmeter.

Disclaimer : some people might say that a battery should always be tested under load but I have found that in most common household applications this is insignificant and will not change the results of the testing too much.

Things that you will need : Voltmeter Alkaline battery

Basic facts : The proper voltage for AA/AAA alkaline battery is 1.5V The proper voltage for AA/AAA NiCd/NiMh rechargeable battery is 1.25 Volts

To test the battery, turn on your voltmeter, put the voltmeter on DCV and make sure that it is far above the battery voltage, on most voltmeters there is a setting 20 in the DCV area, so switch your voltmeter to that setting.

With the battery in front of you, put the red probe to battery’s nipple and the black probe to the battery’s flat side (-). Notice the voltage reading on the voltmeter.

If the reading is more than 1.3V for alkaline battery (not rechargeable battery) then the battery still has some juice left in it, don’t throw it away. Otherwise, properly discard of the battery.

Tip : do not use old and new batteries in the same device at the same time. Try to use batteries that have same amount of energy stored in them.

Another tip: I sort my batteries according to Voltages, 1.35 Good, 1.2V-1.3V Ok (but almost out), 1V-1.2V Discard.

I will attach some pictures of measurements in action.

Instructions on how to use a multimeter are out of scope of this Instructable, you can find some information here: http://www.ladyada.net/learn/multimeter/

Did you make this project? Share it with us!

## Комментарии и мнения владельцев

Today I had a major name-brand digital thermostat fail, driving my house temperature to 80° before the failure was caught, wasting a lot of expensive energy as well. The thermostat is battery powered, and when checking the two AA’s it uses, the voltage on each was 1.32 and 1.33V, respectively. in some cases, that voltage may be usable, but in this application it was insufficient to power the relay that shuts off the furnace. Just be very careful of your particular application.

Was you furnace stuck on when the cells failed?

This is not a totally foolproof way to check cells, and you are certainly right to advise folks to be thoughtful and prudent about where they put their faith. Obviously I haven’t personally examined your home climate control system, so I’d be a fool to spout off and tell you there’s been a mistake. But I have to say that something seems amiss here.

I don’t mean to insult your intelligence, and if you know your stuff and are certain about what happened, please forgive me. But in case you’re not too familiar with HVAC and are just guessing, I want to give you a heads-up that the problem could be something else and you may want to be on the lookout. Although it appeared a low battery was your problem, it could be that the fresh battery, (or the some aspect of the battery change) just masked or reset a different problem.

I am not an HVAC pro or guru; my observations are not definitive. Prelude over. There are two things that seem unusual to me, and here’s what I can tell you. Although electronic thermostats do (usually, anyway) rely on their own power source to run their internals (including a switch that determines whether the furnace will be told to run), the actual messenger that switches it on is typically a ~5V line which is supplied by a transformer in the furnace. The thermostat’s power just has to decide to close a little circuit on its board, which doesn’t usually take much juice. Granted, that doesn’t prove anything. The thing that bugs me more is thatit’s usually a closed circuit that turns a unit on. Lack of power should result in a unit that fails to turn on.

I won’t pretend that I can tell you what else could have been at fault for the stuck on condition, or even that I know for certain it wasn’t just as you said. I just wanted to help out by telling you that from here it looks like there might be another problem lurking. If you know something I don’t, I’d be happy to have you educate me.

Thanks, or you’re welcome. Or both.