How To Wire 3 12v Batteries For 36v?

Before we even start talking about how to wire 3 12v batteries for 36v, you should know a little bit about how a single battery works. Most lead-acid batteries consist of six cells, each with a nominal voltage of 2.1 volts.

These cells are joined end-to-end in a series arrangement called a “string.” The purpose of multiple batteries wired together is to produce higher voltages for use by the motor controller or load.

Larger lead-acid batteries will simply have more cells, and therefore be able to provide the required voltage needed by the system.

Connecting batteries together to form a battery bank can be very simple or quite complex, depending on the system design.

A series connection works well for many 36-volt systems. It can be very simple to establish, but also very simple to destroy if done improperly.

When building an electrical system for your RV, you are probably going to have to deal with more than one battery at some point.

You can connect batteries together in series or parallel. Connecting batteries so their voltages add is called series connection and connecting batteries so their amp-hours will add is called parallel.

In this post, I am going to tell you how to wire 3 12v batteries for 36v in detail.

How Do You Wire 3 12v Batteries For 36v – Easy Method

How to Wire 3 12V Batteries for 36V

  • Step 1

    Install all 3 of your 12V batteries together, side by side. Make sure the negative terminal of one is connected to the positive terminal of another.
    When you look at it from this perspective, you can see that all three are upside down, or negative end up.

  • Step 2

    The second step is to connect the positive (red) jumper cable from your inverter/charger to the first battery’s positive (top), and the black negative cable to the last batteries’ negative terminal (bottom).

  • Step 3

    Now go to the 2nd battery, and connect its positive cable with the next battery’s negative connection.

  • Step 4

    Repeat this process until you have connected all three batteries together in series with your jumper cables. Keep in mind that your jumper cables are now creating a circle of energy transfer. This is what they call ‘daisy-chaining.

  • Step 5

    The last step is to connect the negative cable from your inverter/charger to the clean, metal part of the first battery’s chassis. This will complete your circuit and create 36 volts across all 3 batteries wired together in series.

Warning!  Never wire batteries together without first connecting them to isolated ground. This can cause a dangerous hydrogen gas explosion, which is how most batteries are made anyway!

You should always make sure you have an adequate fuse or circuit breaker between your power source and the inverter/charger.

Note:  Before you connect the batteries, it is recommended that you read the manufacturer’s instructions as all batteries have slightly different procedures for charging and connecting.

What are the Precautionary measures while wiring 3 12v batteries in series for 36 volts?

Here are some precautionary measures while wiring 3 12v batteries in series.

If you wire three 12-volt batteries together, the voltage will increase from 12 volts to 36 volts. The drawback is that your amperage will decrease.

This means you’ll need a larger inverter if you want to run appliances off this 36-volt bank instead of a smaller one because there’s a trade-off between voltage and amperage.

When wiring batteries in series, you will not add the voltage of all three batteries. You only add the voltage from one battery to another. If you have 12 volt 100 amp-hour batteries, then when wired together in series for 36 volts, they will combine for an output of 400 amp-hours at 36 volts.

When you wire batteries in series, they must be identical. This means that they were all manufactured the same way, with their internal parts and equally matched capacities at the time of your purchase.

Do not mix old batteries with new ones, for instance; this could cause uneven charging or discharging of your bank due to differences in voltage potentials and self-discharge rates.

These batteries must also be fully charged and tested before they are interconnected, to ensure that you do not wire bad or weak batteries together with good ones.

The last thing you want is for one battery to fail and ruin the whole series circuit; this can cause fires if not carefully monitored.


Wiring three 12v batteries in series is a simple process that provides an easy way to increase the voltage of your bank. Just make sure you wire them properly, using isolated ground and testing to ensure they are identical before connecting.

In the end, you should always make sure that you wire your batteries safely and appropriately to ensure safety. Wiring 3 12v batteries together is a great way to create more power for your appliances while maintaining the ability to keep them running.

The above information is mostly based on personal experience. I hope you found the facts provided useful and if so please let me know in the comments below.

Frequently Asked Questions

Why do you need 3 12v batteries for 36v?

If you only have one 12v battery then it will not produce enough power to run your appliances. By wiring 3 12v batteries in series, the resulting voltage is 36 volts which is more than enough to run most appliances.

Can you put 3 12v batteries in a 36v golf cart?

You can but it would be very dangerous. If you connect the batteries in series without first connecting them to isolated ground, this could cause a dangerous hydrogen gas explosion.

Can you wire 3 12-volt batteries in parallel?

Yes, you can wire 3 12-volt batteries in parallel. The voltage remains at 12 volts, but the capacity increases to 1800 amps-hour since you now have three 100 amp-hour batteries instead of one. This makes for a much safer battery bank.

Can you wire lead-acid batteries with lithium-ion?

Yes, but they do not work well together because of their voltage difference. It’s best to just wire them differently, but it is possible to mix their voltages using a 24v-to-12v step-down transformer.

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