How to connect batteries in series and parallel
If you have ever worked with batteries you have probably come across the terms series, parallel, and series-parallel, but what exactly do these terms mean?
Series, Series-Parallel, and Parallel is the act of connecting two batteries together, but why would you want to connect two or more batteries together in the first place?
By connecting two or more batteries in either series, series-parallel, or parallel, you can increase the voltage or amp-hour capacity, or even both; allowing for higher voltage applications or power hungry applications.
CONNECTING BATTERIES IN SERIES
Connecting a battery in series is when you connect two or more batteries together to increase the battery systems overall voltage, connecting batteries in series does not increase the capacity only the voltage. For example if you connect four 12Volt 26Ah batteries you will have a battery voltage of 48Volts and battery capacity of 26Ah.
To configure batteries with a series connection each battery must have the same voltage and capacity rating, or you can potentially damage the batteries. For example you can connect two 6Volt 10Ah batteries together in series but you cannot connect one 6V 10Ah battery with one 12V 20Ah battery.
To connect a group of batteries in series you connect the negative terminal of one battery to the positive terminal of another and so on until all batteries are connected. You would then connect a link/cable to the negative terminal of the first battery in your string of batteries to your application, then another cable to the positive terminal of the last battery in your string to your application.
When charging batteries in series, you need to use a charger that matches the battery system voltage. We recommend you charge each battery individually to avoid battery imbalance.
Sealed lead acid batteries have been the battery of choice for long string, high voltage battery systems for many years, although lithium batteries can be configured in series, it requires attention to the BMS or PCM.
CONNECTING BATTERIES IN PARALLEL
Connecting a battery in parallel is when you connect two or more batteries together to increase the amp-hour capacity. With a parallel battery connection the capacity will increase, however the battery voltage will remain the same.
Batteries connected in parallel must be of the same voltage, i.e. a 12V battery can not be connected in parallel with a 6V battery. It is best to also use batteries of the same capacity when using parallel connections.
For example, if you connect four 12V 100Ah batteries in parallel, you would get a 12V 400Ah battery system.
When connecting batteries in parallel, the negative terminal of one battery is connected to the negative terminal of the next and so on through the string of batteries. The same is done with positive terminals, i.e. the positive terminal of one battery to the positive terminal of the next.
For example, let’s say you needed a 12V 300Ah battery system. You will need to connect three 12V 100Ah batteries together in parallel.
Parallel battery configuration helps increase the duration in which batteries can power equipment, but due to the increased amp-hour capacity they can take longer to charge than series connected batteries. This time can safely be reduced, without damaging the batteries, by charging faster. Now that the battery is larger, a higher current charge is still the same percentage of the total capacity, and each battery ‘feels’ a smaller current.
While it is often debated what the best way to connect in parallel is, the above method is common for low current applications. For high current applications, talk to one of our experts as your situation may need a special configuration to ensure all of the batteries age at as similar as possible rates.
Battery Charge Time Calculator
Use our battery charge time calculator to easily estimate how long it’ll take to fully charge your battery.
Tip: If you’re solar charging your battery, you can estimate its charge time much more accurately with our solar battery charge time calculator.
How to Use This Calculator
Enter your battery capacity and select its units from the list. The unit options are milliamp hours (mAh), amp hours (Ah), watt hours (Wh), and kilowatt hours (kWh).
Enter your battery charger’s charge current and select its units from the list. The unit options are milliamps (mA), amps (A), and watts (W).
If the calculator asks for it, enter your battery voltage or charge voltage. Depending on the combination of units you selected for your battery capacity and charge current, the calculator may ask you to input a voltage.
Select your battery type from the list.
Optional: Enter your battery state of charge as a percentage. For instance, if your battery is 20% charged, you’d enter the number 20. If your battery is dead, you’d enter 0.
Click Calculate Charge Time to get your results.
Battery Charging Time Calculation Formulas
For those interested in the underlying math, here are 3 formulas to for calculating battery charging time. I start with the simplest and least accurate formula and end with the most complex but most accurate.
Formula: charge time = battery capacity ÷ charge current
The easiest but least accurate way to estimate charge time is to divide battery capacity by charge current.
Most often, your battery’s capacity will be given in amp hours (Ah), and your charger’s charge current will be given in amps (A). So you’ll often see this formula written with these units:
charge time = battery capacity (Ah) ÷ charge current (A)
However, battery capacity can also be expressed in milliamp hours (mAh), watt hours (Wh) and kilowatt hours (kWh). And your battery charger may tell you its power output in milliamps (mA) or watts (W) rather than amps. So you may also see the formula written with different unit combinations.
charge time = battery capacity (mAh) ÷ charge current (mA) charge time = battery capacity (Wh) ÷ charge rate (W)
And sometimes, your units are mismatched. Your battery capacity may be given in watt hours and your charge rate in amps. Or they may be given in milliamp hours and watts.
In these cases, you need to convert the units until you have a ‘matching’ pair.- such as amp hours and amps, watt hours and watts, or milliamp hours and milliamps.
For reference, here are the formulas you need to convert between the most common units for battery capacity and charge rate. Most of them link to our relevant conversion calculator.
Battery capacity unit conversions:
- watt hours = amp hours × volts
- amp hours = watt hours ÷ volts
- milliamp hours = amp hours × 1000
- amp hours = milliamp hours ÷ 1000
- watt hours = milliamp hours × volts ÷ 1000
- milliamp hours = watt hours ÷ volts × 1000
- kilowatt hours = amp hours × volts ÷ 1000
- amp hours = kilowatt hours ÷ volts × 1000
- watt hours = kilowatt hours × 1000
- kilowatt hours = watt hours ÷ 1000
Charge rate unit conversions:
The formula itself is simple, but taking into account all the possible conversions can get a little overwhelming. So let’s run through a few examples.
Example 1: Battery Capacity in Amp Hours, Charging Current in Amps
Let’s say you have the following setup:
- Battery capacity: 100 amp hours
- Charging current: 10 amps
To calculate charging time using this formula, you simply divide battery capacity by charging current.
In this scenario, your estimated charge time is 10 hours.
Tip: You can estimate how much battery capacity you need by using the inverse of this formula: amps × hours = amp hours.
Example 2: Battery Capacity in Watt Hours, Charging Rate in Watts
Let’s now consider this scenario:
Because your units are again ‘matching’, to calculate charging time you again simply divide battery capacity by charging rate.
In this scenario, your estimated charge time is 8 hours.
Example 3: Battery Capacity in Milliamp Hours, Charging Rate in Watts
Let’s consider the following scenario where the units are mismatched.
First, you need to decide which set of matching units you want to convert to. You consider watt hours for battery capacity and watts for charge rate. But you’re unable to find the battery’s voltage, which you need to convert milliamp hours to watt hours.
You know the charger’s output voltage is 5 volts, so you settle on amp hours for battery capacity and amps for charge rate.
With that decided, you first divide watts by volts to get your charging current in amps.
Next, you convert battery capacity from milliamp hours to amp hours by dividing milliamp hours by 1000.
Now you have your battery capacity and charging current in ‘matching’ units. Finally, you divide battery capacity by charging current to get charge time.
In this example, your estimated battery charging time is 1.5 hours.
Formula: charge time = battery capacity ÷ (charge current × charge efficiency)
No battery charges and discharges with 100% efficiency. Some of the energy will be lost due to inefficiencies during the charging process.
This formula builds on the previous one by factoring in charge/discharge efficiency, which differs based on battery type.
Energizer Recharge Value AA/AAA NiMH Battery Charger review
How many devices, toys and gadgets do you own that use AA or AAA batteries? Do you feed these devices standard alkaline batteries, or do you use rechargeables? I personally prefer to go the rechargeable route mainly because it’s easier and less expensive for me to pop a set of drained batteries into a charger and wait for them to rejuice, then it is for me to drive to the store and buy a brand new set. I’ve been using an ancient Realistic (Radio Shack) branded charger for years and although it charges batteries just fine, it’s bulky and not efficient because it continues to charge the batteries even after they are fully charged. When the folks at Energizer asked if I would like to review one of their chargers, I gladly accepted and they sent me a sample of their new Recharge Value AA/AAA NiMH Battery Charger. Let’s take a look.
Note: Images can be clicked to view a larger size.
What’s in the package?
Energizer charger 4 AA NiMH 1300 mAh batteries Instruction sheet
This charger is designed to accommodate 4 AA or 4 AAA Nickel Metal Hydride (NiMH) batteries. You can not use this charger to charge other types of batteries such as Lithium Ion and standard alkaline cells. It will allow you to mix sizes, so you can charge 2 AA’s and 2 AAA’s at one time as long as you make sure that each battery type is of the same mAh rating. However, you can’t charge an odd number of batteries such as 1 or 3 cells.
The Value charger comes with 4 AA 1300 mAh pre-charged batteries. I was surprised to see the low 1300 mAh rating on the included batteries considering that Energizer also offers 2300 mAh batteries.
The charger itself is compact and attractive.
It has fold down prongs, which allow it to easily store in a drawer or gear bag.
One feature I really love is the hole that goes straight through the charger. How many times have you used a screwdriver or another pointy object to help you remove batteries from a charger? Removing batteries from the Recharge Value charger is much easier because you can just push them out with your fingers.
The other feature that I like is the large status indicator, which glows red while charging, green when finished and flashes red when a bad battery has been detected.
During the time that I’ve been testing this charger, I’ve used it to charge the included batteries as well as another set of Energizer AA’s that I already had on hand. As luck would have it, I didn’t have any other brands of batteries to test.But the charger should work just fine as long as the batteries do not exceed 2650mAh for AA’s and 1000mAh for AAA’s.
It’s important to note that this is not a Smart charger. It’s actually a timer-based dumb charger. What’s the difference and why should you care? A Smart charger monitors the voltage of each cell individually during charging and stops when a charge-termination signal (negative delta-Voltage) is detected. This avoids over-charging. A Dumb charger relies on a timer to stop charging or has no termination mechanism at all. This usually results in over-charging which is bad for battery lifespan.
The Energizer Recharge Value Charger charges at a fixed current (300mA for AA, 150mA for AAA) for a fixed time of 11 hours. No matter what the actual capacity and status of your batteries, it will charge for that length of time and will then turn off. When you use it to recharge the included 1300mAh batteries, you have to remember to remove them after 5-6 hours (because 1300mAh/300mA = ~5.5 hours). If you forget and leave them in the charger until the auto timer turns off after 11hrs, those batteries will be over-charged by over 50%. That doesn’t mean the batteries will explode or catch fire, but it can negatively impact the overall life of the batteries.
Should you buy the Energizer Recharge Value AA/AAA NiMH Battery Charger? I wish that it was a Smart charger with the capability of not over charging each individual battery because I really like this charger for the main two reasons I mentioned above: easy battery removal and large status LED. As is, you’re probably better off spending a few extra dollars on a Smart charger so that you’ll get more rechargers per battery, which will save you more money and energy in the long run. I’m going to continue to use this one because it’s less bulky than my old one and it’s easier to remove the batteries. However, I’m going to search around for a similarly sized Smart charger.
03/05/13: Update from Energizer
The Value Charger does include delta voltage detection to avoid over charging. It monitors the voltage to determine when the batteries are full and will then automatically shut off. The green light will remain on to serve as an indicator that the batteries are full.
The charge time for the included 1300 mAh AA batteries is about five hours.
The 11-hour timer is strictly a back-up safety feature in the event the charger doesn’t turn off once the batteries are fully charged.
The Value Charger will recharge any NiMH AA and AAA batteries. We recommend using Energizer rechargeable batteries with Energizer chargers.
The best 8-cell battery charger
If you frequently use AAs and AAAs in your electronics, the Powerex MH-C800S 8-Cell Smart Charger will keep your batteries juiced and extend their life.
Pros: 8 charging slots, features conditioning cycle
Cons: Expensive, only charges AA and AAA batteries
The Powerex MH-C800S 8-Cell Smart Charger is manufactured by Maha Energy, an organization that focuses solely on charging and battery technology for both consumer and industrial sectors.
The MH-C800S can charge between one and eight NiMH or NiCd AA or AAA batteries. The LCD screen uses three bars to show the charging status of each battery. There are three charge modes: Rapid charge (one to two hours), soft charge (three to four hours), and conditioning, which can take a full day.
Wirecutter previously recommended the Powerex charger for people who need eight charging slots on one outlet. The reviewer appreciated the accurate charging, that you can monitor the progress, and it’s easy to use. However, he didn’t like that the default mode is the faster 1-A charging, which isn’t as conducive to extending your battery’s lifespan as the Soft charge.
The best battery charger for vaping
At a relatively low price point, the XTAR VC4 Charger is able to charge a wide range of battery sizes and types.
Pros: Charges several different battery types, cost-effective, USB power input
Cons: Doesn’t come with a USB wall adapter, it takes some work to fit AAA batteries in
There are a couple of features that set the XTAR VC4 Charger apart from other devices in our guide. First, it doesn’t plug directly into the wall. The charger features a USB charge cable, which you can plug into just about anything with a USB port. I use a multiple-port USB wall adapter. Another unique feature is that the slots are large enough to fit D-cell batteries. It’s fairly rare to find a unit that can handle NiMH cells ranging from AAA to D.
XTAR sent me the VC4 for free to test out, and for the most part my family has been happy with it. I use it for charging NiMH batteries for a variety of devices, including my sons’ toys, and my wife uses it for her vaporizer’s 18650s.
I’ve found that it’s a real pain trying to get the AAA batteries in there just right to get them to charge. Other sizes seem to work fine, though. The display is easy to read and gives helpful information that even a layperson can understand, but it can be finicky when you first insert the batteries.
The best for AA and AAA batteries
If you are mainly in need of a good charger for AA and AAA batteries and don’t need a fast charge, consider the affordable Panasonic Advanced Individual Cell Battery Charger Pack.
Pros: Uses slow charge to extend battery life, simple to use, inexpensive, comes with batteries
Cons: Only charges AA and AAA batteries
The Panasonic K-KJ17MCA4BA Advanced Individual Cell Battery Charger Pack is unique in its simplicity. You just pop in one to four AA or AAA batteries (any combination will work) and wait for the charging light to turn off. The batteries charge at a slower 300 mA speed, which is great for extending their lifespan. And, when charging is complete, it automatically shuts off.
There are four different packs that vary based on what batteries come with it. There are the packages that come with four AA or four AAA batteries. The Power Pack comes with 8 AA, 2 AAA, and 2 C-size and D-size spacers. You simply put an AA battery in the spacer when you want to power devices that require C or D cells. The Super Power Pack is essentially the same as the Power Pack, only it has 12 AA and 4 AAA batteries along with the spacers. The charger is the same for all four packages.
The Panasonic Advanced Individual Cell Battery Charger was previously the top pick on Wirecutter. The reviewer liked how simple it is to use and that you can charge just one battery, rather than having an even number in the slots. For the typical NiMH AA battery, he found it took about seven hours to reach a full charge.
Check out our other related buying guides
The best rechargeable batteries
The best rechargeable batteries are high-quality, ready to use out of the package, hold a charge after months in storage, and are economical in the long-term for powering various devices. These are our top picks.
The best charging cables
A great charging cable ensures that your device is always charged up and ready for the day — without breaking. These are our top picks for the best charging cables.
The best Smart outlets
Smart outlets are about convenience and safety: They let you remotely power-down devices unintentionally left plugged-in, and automatically switch on lamps, radios, air conditioners, and more. These are the best Smart outlets.
Joe was a Senior Tech Editor for Insider Reviews with more than a decade of experience in games and tech media. His work has appeared in TechRadar, PC Magazine, Laptop Magazine, Tom’s Guide, AOL’s Games.com, and more. Joe has also appeared as a tech expert on programs such as Cheddar from the floor of the New York Stock Exchange as well as on panels of experts for events such as CES. His specialties include computing as well as gaming products using a variety of operating systems and interfaces, not to mention extensive benchmarking experience. Learn more about how our team of experts tests and reviews products at Insider here. Learn more about how we test tech and electronics.
Antonio is a senior tech reporter for Insider’s Reviews team, where he helps lead coverage, reviews, and guides of smartphones, tablets, accessories, wearables, Smart home products, as well as audio devices from Apple, Google, Samsung, OnePlus, and other major tech companies. Before joining Business Insider, Antonio was a consumer-electronics analyst at PCMag. He graduated from Colgate University in 2009 with a bachelor’s degree in history. You can contact Antonio with tips and cool tech via email at: email@example.com Learn more about how our team of experts tests and reviews products at Insider here. Learn more about how we test tech and electronics.
Sign up for Insider Reviews’ weekly newsletter for more buying advice and great deals.
You can purchase logo and accolade licensing to this story here.
Disclosure: Written and researched by the Insider Reviews team. We highlight products and services you might find interesting. If you buy them, we may get a small share of the revenue from the sale from our partners. We may receive products free of charge from manufacturers to test. This does not drive our decision as to whether or not a product is featured or recommended. We operate independently from our advertising team. We welcome your feedback. Email us at firstname.lastname@example.org.