How to Wire 12V Batteries in Series & Parallel (w/ Photos!)

In this tutorial, I’ll show you step-by-step how to wire batteries in series and parallel, as well as how to combine the two to create series-parallel combinations. I’ll also cover when to use series or parallel wiring.

Click on a wiring method to jump to its instructions:

6 Things to Know Before Wiring Batteries in Series & Parallel

  1. Your batteries should be identical. They should have the same voltage and capacity. They should be the same age and from the same brand. Because brands may make changes to their batteries and BMS’s over time, you should also buy them around the same time. (There are certain situations where you can use dissimilar batteries, but I won’t cover those in this tutorial.)
  2. All your batteries should be at the same state of charge before you wire them together. The easiest way to do this is to buy a compatible battery charger and separately charge all of them to 100%. You can also solar charge them if you’re into DIY solar.
  3. Buy the right battery cables for your battery. The battery cables should fit your batteries’ terminals, and they should be the right wire gauge for handling the maximum amount of current your device(s) will draw.
  4. For parallel connections, your battery cables should be the same length. This helps ensure each battery can split the current equally.
  5. Before connecting your batteries, identify the positive and negative terminals on each. On most batteries, the terminals will be color-coded red for positive (+) and black for negative (-).
  6. Don’t exceed the max series and parallel string lengths of your batteries. Most batteries have stated limits regarding how many of them can be wired in series and parallel. For instance, with 12V LiFePO4 batteries, it’s common for them to be able to handle up to 4 batteries wired in series, and up to 4-10 wired in parallel. Look in your battery’s product manual or spec sheet for these limits.

How to Wire Batteries in Series

Wiring batteries in series sums their voltages and keeps their amp hours the same. It’s particularly useful for wiring two 6V lead acid batteries, or four 3.2V lithium cells, to make a 12V battery.

Series connections can also be used to wire multiple 12V lead acid or lithium batteries together to make a 24V, 36V, or 48V battery bank, which is useful in DIY and off-grid solar applications.

Parts & Tools

Step 1: Connect the Negative Terminal of One Battery to the Positive Terminal of Another

Connect the battery cable to the negative terminal of one battery. To do so, use a ratchet or screwdriver to unscrew the terminal’s bolt. Thread the cable’s ring terminal through the bolt, then screw the bolt back on the terminal.

Note: Some people prefer to use black cables for series connections, others prefer red. I prefer black, but there’s no right or wrong choice. Just use the color of cable you prefer or have on hand.

Connect the other end of the battery cable to the positive terminal of another battery.

That’s it! Your batteries are now wired in series. You’ll often hear connected batteries referred to as a “string” of batteries. So now you have a series string of 2 batteries.

If you want, check your battery bank’s voltage with a multimeter. Because I wired two 12V batteries in series, I expect to measure a voltage of around 24 volts. (In reality, a 12V LiFePO4 battery’s resting voltage will usually be closer to 13-13.5 volts, so I’d expect a voltage of around 26-27 volts.) I got 26.4 volts, which is exactly in line with expectations.

Check! My two 12V 100Ah batteries are now wired in series, resulting in a 24V 100Ah battery bank.

Note: If you don’t want to bother with wiring batteries yourself, many brands offer pre-made 24V batteries and 48V batteries.

Step 2: Repeat as Needed

If your battery allows it, you can repeat the above steps to connect more batteries in series.

You can wire three 12V batteries in series to create a 36V battery bank. Once again, just connect the negative terminal of your 2-battery series string to the positive terminal of the third battery.

And, once again, you can use a multimeter to check that the voltage is around 36 volts. I got 39.7 volts, so I know my 3 batteries are correctly connected in series.

You can wire a fourth battery in series following the same steps. My batteries can handle up to 4 wired in series, so let’s do one last one for good measure.

And we’ll check the battery bank’s voltage with a multimeter, expecting a voltage of around 48 volts. I got 52.9 volts, so we’re good to go.

Done! Like I said, you can wire as many in series as your batteries allow for. LiFePO4 batteries are often limited to 4 batteries in series to protect the BMS. However, there are some that can’t be wired in series, such as the Renogy 12V 100Ah Smart Lithium Iron Phosphate Battery. Be sure to check!

How to Wire Batteries in Parallel

Wiring batteries in parallel sums their amp hour capacities and current limits and keeps their voltage the same.

Parallel wiring is useful when you want to keep your battery voltage the same — such as when you’re powering 12V devices directly off a 12V battery — while increasing runtime and current limits.

Parts & Tools

Step 1: Connect the Positive Terminal of One Battery to the Positive Terminal of Another

Use a battery cable to connect the two batteries’ positive terminals together. I recommend using a red battery cable for this connection.

Step 2: Connect the Negative Terminal of the First Battery to the Negative Terminal of the Other

Use a second battery cable to connect the two batteries’ negative terminals together. I recommend using a black battery cable for this connection.

Your 2 batteries are now wired in parallel. This is what people mean when they say you wire batteries in parallel by connecting positive to positive and negative to negative.

In this example, I wired two 12V 100Ah batteries in parallel to get a 12V 200Ah battery bank. Because parallel connections don’t affect voltage, there’s no way to use a multimeter to check the connection.

If you want, you can do a capacity test. That requires some extra equipment, though, so I won’t cover that here.

Note: If you don’t want to wire batteries in parallel yourself, many battery brands also sell 12V batteries in 200Ah, 300Ah, and 400Ah sizes.

Step 3: Repeat as Needed

If your batteries allow it, you can repeat the above steps to connect even more batteries in parallel.

To connect a third, again wire positive to positive and negative to negative. This results for me in a 12V 300Ah battery bank.

To connect a fourth, repeat the connections. Now I have a 12V 400Ah battery bank.

Done!

How to Wire Batteries in Series-Parallel

You can use a combination of series and parallel connections to make a battery bank with your desired voltage and capacity. There are many different series-parallel wiring configurations you can choose from. I’ll cover the simplest in this tutorial.

Series-parallel wiring can get confusing. It pays to research and ask around for help on online forums if you’re unsure how your specific setup should be wired.

Parts & Tools

Step 1: Wire Your Batteries in Series Strings of Equal Length

Decide what voltage you want your battery bank to have. For this example, I’ll go with 24 volts. I’m using 12V batteries, so that means each of my series strings needs to be 2 batteries in length.

Wire your batteries in series strings of equal length. I have 4 batteries, so I wired them in 2 strings, each of which has 2 batteries wired in series.

If you want, check the voltage of each string with a multimeter. In this case, I’d expect mine to read something close to 24 volts.

Now I have two 24V 100Ah battery banks, and I can connect them in parallel to expand their amp hour capacity.

Step 2: Wire Your Series Strings in Parallel

Wire the 2 series strings in parallel by connecting positive to positive and negative to negative.

If you want, check the voltage of your finished battery bank with a multimeter. I wired two 24V 100Ah battery banks in parallel to get a 24V 200Ah battery bank, so I expect a voltage of around 24 volts. I got 26.4 volts, which is exactly as expected.

Done! You can use these principles to wire even more batteries into different series-parallel combinations.

Note: A shorthand that people use to describe a battery bank’s wiring configuration is to list the number of batteries wired in series followed by the letter “s” and then the number of batteries wired in parallel followed by the letter “p”. For instance, I just created a 2s2p battery bank. Some LiFePO4 batteries can be wired into as big as 4s4p configurations.

How Wiring in Batteries in Series & Parallel Affects Voltage & Capacity

Wiring batteries in series sums their voltages while keeping their amp hour capacity the same. Wiring two 12V 100Ah batteries in series gives you a 24V 100Ah battery bank.

12V + 12V = 24V

Wiring batteries in parallel sums their amp hour capacities while keeping their voltage the same. Wiring two 12V 100Ah batteries in parallel gives you a 12V 200Ah battery bank.

100Ah + 100Ah = 200Ah

Amp Hours vs Watt Hours

Amp hours (Ah) and milliamp hours (mAh) are commonly used to describe battery capacity. 1 amp hour equals 1000 milliamp hours. However, the total amount of energy a battery can deliver is best expressed in watt hours (Wh), which is equal to a battery’s amp hours times its voltage.

Formula: watt hours = amp hours × voltage

Calculator: Amp Hours to Watt Hours Calculator

What this means is that, regardless of how you wire your batteries together, you’re increasing the total watt hours of your battery bank. A 24V 100Ah battery bank and a 12V 200Ah battery bank both have 2400 watt hours.

24V × 100Ah = 2400Wh

12V × 200Ah = 2400Wh

You can use our battery capacity calculator to calculate the amp hour or watt hour capacity of your battery given how many batteries you have wired in series and parallel.

When to Wire Batteries in Series vs Parallel

Series

  • You want to save money on wiring and equipment such as solar charge controllers. Series wiring increases voltage which helps keep current (amperage) low. Wire and other electrical equipment get more expensive the higher their current ratings get. That being said, electrical equipment also has voltage ratings, so be careful not to exceed these, either. Voltage ratings tend to be higher, though, and you don’t as often need to worry about them in DC electrical systems.
  • You can raise voltage while still powering your devices. Often, you’ll want to power a device directly off the battery. For instance, you may want to connect 12V LED lights or a 12V inverter to your 12V battery. Devices have acceptable voltage ranges — 12V LED lights might be able to accept 11-15V, for instance — so wiring in series is best when you can raise battery voltage without exceeding the acceptable input voltages of your devices. If you’re connecting your batteries to a solar charge controller, also check that the charge controller is rated for the higher battery voltage.

Parallel

  • You want to increase runtime while keeping your battery bank voltage the same. Parallel wiring increases amp hour capacity while keeping voltage the same, meaning your battery bank will last longer while still being able to power the same devices.
  • You want to increase your battery’s max charge and discharge rates. Batteries have recommended charge and discharge rates, which are based on their amp hour capacity. For instance, most 100Ah LiFePO4 batteries have a recommended max continuous charge rate of 50 amps, and most 100Ah lead acid batteries have a recommended max continuous charge rate of 30 amps. Because these rates are based on battery amp hours, you can increase them by adding more batteries in parallel. You can estimate charge time using our battery charge time calculator.
  • You want to lower your battery’s C-rate. How fast a battery charges and discharges can be expressed as something called a C-rate. Different types of batteries have different recommended C-rates for charging and discharging, and exceeding these can shorten your battery’s lifespan or affect how many amp hours the battery actually outputs. You can lower your battery’s C-rate by expanding your battery bank’s amp hour capacity while keeping charing and discharging currents the same.
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Alex Beale
Alex Beale
Alex Beale is the founder and owner of Footprint Hero. As a self-taught DIY solar enthusiast, Alex has spent 4 years producing educational solar content across YouTube, TikTok, Instagram, and the Footprint Hero blog. During that time, he's built Footprint Hero to over 7 million blog visits and 18 million YouTube views. He lives in Tennessee.