Learning, Wiring,

How to Wire 3 12v Batteries for 36v (6-Step Guide)

By the end of this guide, you should be able to wire three 12v batteries together to achieve 36 Volts.

There are many scenarios where wiring together 3 12v batteries has really helped me, including on my boat and getting my trolling motor going. I think it’s important to do this correctly to avoid frying your battery. Apart from that, you can apply most of this logic to wiring more or fewer batteries in series.

Since 36V is the most common wiring type, I’m going to explain how to wire 3 12V batteries for 36V.

In summary, to wire three 12V batteries for 36V, follow these steps.

  • Install or place all three batteries side by side.
  • Connect the 1st battery’s negative terminal to the 2nd one’s positive terminal.
  • Connect the 2nd battery’s negative terminal to the 3rd one’s positive terminal.
  • Use a multimeter to check the voltage of the battery pack.
  • Take the inverter/charger and connect its positive wire to the positive terminal of the 1st battery.
  • Connect the negative wire of the inverter/charger to the negative terminal of the 3rd battery.

We’ll be going through this in more detail below.

Difference Between the Series and Parallel Connection

Good knowledge of series and parallel connections will come in handy in many occasions. For this demonstration, we use a series connection. However, a bit of extra knowledge won’t hurt you. So, here is a simple explanation of these two connections.

Series Battery Connection

electric cells in series
Video | infinity sci

Connecting two batteries using the 1st battery’s positive terminal and the 2nd battery’s negative terminal is known as a series battery connection. For instance, if you connect two 12V, 100Ah batteries in a series connection, you’ll get 24V and 100Ah as the output.

Parallel Battery Connection

electrical cells in parallel
Video | infinity sci

In a parallel connection, the two positive terminals of the batteries will be connected. Also, the negative terminals of the batteries will be connected too. In this kind of connection, you’ll get 12V and 200Ah as the output.

Simple 6-Step Guide to Wire 3 12V Batteries for 36V

Things You’ll Need

  • Three 12V batteries
  • Two jumper cable
  • Digital Multimeter
  • Wrench
  • Fuse

Step 1 – Install the Batteries

First and foremost, install/place the batteries side by side. Place the 1st battery’s negative terminal adjacent to the 2nd one’s positive terminal. Study the above-given image for a proper understanding.

Step 2 – Connect the 1st and 2nd Batteries

Then, connect the 1st battery’s negative terminal to the 2nd one’s positive terminal. Use a jumper cable for this. Loosen the screws of the battery terminals and place the jumper cable on them. Next, tighten the screws.

Step 3 – Connect the 2nd and 3rd Batteries

This step is quite similar to step 2. Connect the 2nd battery’s negative terminal to the 3rd one’s positive terminal. Use the second jumper cable for this. Follow the same process as in step 2.

Step 4 – Check the Voltage

Take the multimeter and set it to voltage mode. Then, set the multimeter’s red probe to the 1st battery’s positive terminal. Next, set the black probe on the 3rd battery’s negative terminal. If you did follow the above process correctly, the multimeter should show a reading above 36V.

Step 5 – Connect the Inverter and the 1st Battery

After that, connect the positive wire of the inverter to the positive battery terminal of the 1st battery.

Remember to use a suitable fuse for this connection. Using a fuse between the power source and the inverter is ideal for safety. (1)

Step 6 – Connect the Inverter and the 3rd Battery

Now connect the negative wire of the inverter to the 3rd battery’s negative terminal.

A Few Things to Consider While Wiring Three 12V Batteries in a Series Connection

Even though the above process is straightforward, there are a few important facts to consider while wiring three 12V batteries together.

Selection of the Batteries

Always choose three identical batteries for this task. That means you should buy three batteries that are manufactured by the same company or the same way. Also, the capacities of these three batteries should be the same.

Don’t Mix the Batteries

Never use a brand new battery with a used battery. The charge of the batteries might vary. So, using three new batteries for your trolling motor is better.

Check the Batteries Before You Start

Individually check the voltages of the three batteries with a digital multimeter before starting the wiring process. The voltage should be above 12V. Don’t use weak batteries for this process.

Keep in mind: One bad battery can ruin the whole experiment. So, make sure that doesn’t happen.

Should I Choose a 36V Battery or Three 12V Batteries?

One might think using one 36V battery is a far better technique than using three 12V batteries. Well, I can’t argue with that point. But I can give some pros and cons of using three 12V batteries.


  • If one of the 12V batteries fails, you can easily replace them.
  • Having three batteries help the weight distribution of the boat.
  • For three 12V battery systems, you don’t need a special charger. But for 36-volt batteries, you’ll need a dedicated charger.


  • Too many connection points in three 12V battery connections.

Tip: Three Lithium 12V batteries are the best options for a trolling motor.


How to Calculate Wattage of the Three 12V, 100Ah Batteries in a Series Connection?

To calculate wattage, you’ll need the total amperage and voltage.

V = 36 volts
A = 100 amp

According to Joule’s Law,

P = V.I = 36 × 100 = 3600 watt

Therefore, you’ll get 3600 watts as output from these three batteries.

Can I Wire Three 12V, 100Ah Batteries in a Parallel Connection?

Yes, you can connect them. Connect the three positive ends together and do the same for the negative ends. When connecting the three 12V and 100Ah batteries in a parallel connection, you’ll get 12V and 300Ah as the output.

Is it Okay to Wire a Lithium-ion Battery with a Lead-acid Battery?

Yes, you can wire them together. But you might experience some issues due to their voltage difference. The best option is to wire them separately.

How Many Batteries Can I Wire in a Series Connection?

The maximum number of batteries depends on the type of battery and the manufacturer. For instance, you can wire four Battle Born Lithium batteries in a series connection to produce 48V.(2)

Wrapping Up

If you are looking for 24V, 36V, or 48V power output, you now know how to wire batteries in a series connection. But remember, always use a fuse between the power source and the inverter/charger. It will keep your trolling motor safe. The fuse should be able to handle the maximum current of the power source.

Take a look at some of our related articles below.

(1) power source – https://www.britannica.com/technology/power-source
(2) Lithium batteries – https://www.sciencedirect.com/topics/chemistry/

Video References

Tactical WoodGas

infinity sci

The Weekend Angler

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About Sam Orlovsky

AvatarCertifications: B.E.E.
Education: University Of Denver - Electric Engineering
Lives In: Denver Colorado

Electrical engineering is my passion, and I’ve been in the industry for over 20 years. This gives me a unique ability to give you expert home improvement and DIY recommendations. I’m not only an electrician, but I also like machinery and anything to do with carpentry. One of my career paths started as a general handyman, so I also have a lot of experience with home improvement I love to share.

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