How to Connect Six Volt Batteries To Create a 12 Volt Battery Bank

Six volt deep cycle batteries are a popular choice for off-grid solar-powered RV, camper, tiny house, van, or marine use. Two six volt batteries wired in series are needed to create a 12 volt battery bank. But what if you want to increase that capacity? Adding more six volt battery pairs is the solution.

In order to maintain the 12 volt battery bank output and gain more capacity, additional pairs of 6 volt batteries should be connected in parallel to existing battery pairs.

Wed, 05/24/2017 - 19:46 - Series Parallel connection of four six volt deep cycle batteriesFlickr

This type of battery configuration is called series/parallel because each 6 volt battery is connected to another in series, then each pair is connected in parallel.


HOW: Connect positive terminal on battery A1 to negative terminal on battery A2. Repeat this on batteries B1 and B2.

RESULT: The outcome of connecting batteries in series is the that voltage output is added together (12 volts total). The amp hours remain the same.

Example: Two 6 volt batteries rated at 100 amp hours and connected in series will produce 12 volts for 100 amp hours.


HOW: Connect positive output terminal on battery pair A to positive on battery pair B. Connect negative terminal on battery pair A to negative terminal on battery pair B.

RESULT: The outcome of connecting each pair in series is that the output voltage remains the same (12 volts) while the amp hours are added to the overall capacity.

Example 1: Two pairs (each producing 12 volts for 100 amp hours) connected in parallel to another similar pair will produce 12 volts for 200 amp hours

Example 2: Create a 450 amp hour 12 volt battery bank with four 6 volt batteries (demonstrated in the video using four 6 volt 225 amp hours batteries)

  1. Wire the first pair of batteries (A1 and A2) in series to output 12 volts at 225 amp hours
  2. Wire the second pair of batteries (B1 and B2) in series to output an additional 12 volts at 225 amp hours
  3. Wire the two pairs together in parallel for an overall output of 12 volts at 450 amp hours

Fri, 06/09/2017 - 06:56 - Test wiring battery bank in series parallelFlickr

WANT MORE POWER? To increase your amp hour capacity even more, simply add more pairs of 6 volt batteries. For example, adding an additional six volt battery pair will add an additional 225 amp hours for a total of 700 amp hours at 12 volts.

VMAX 225 Amp Hour 6 Volt AGM Batteries

These are the deep cycle batteries (featured in the video) that I installed in my RV

Single Battery (on Amazon)
Set of 4 batteries (on Amazon)
6 Inch #1/0 Battery Cable

These are very thick and well built short battery cables. If you can make these fit, I recommend them. Otherwise go with the 12 cables.

6 Inch RED Cable (on Amazon)
6 Inch BLACK Cable (on Amazon)
12 Inch RED Cable (on Amazon)
12 Inch BLACK Cable (on Amazon)

Dielectric Grease for Battery Connections

I use this stuff to coat all of the metal parts of the battery connections. It helps ensure a good electrical connection and prevents corrosion build up.

Single Tube (on Amazon)

Safety Precautions

It should go without saying that you should follow proper electrical safety practices while working with electricity. For starters, be sure to disconnect all electrical power from your RV before disconnecting or connecting batteries. If you are inexperienced or unsure of your abilities, you should have the work done by a professional.

You should also install proper overcurrent protection (terminal fuses, circuit breakers) and battery disconnect switches on load-serving positive connections to protect you and your equipment. This is not the focus of this article, but I felt compelled to mention it.

Batteries are Heavy

Large deep cycle batteries contain a large amount of lead for storing all of that energy. Therefore they are very heavy. Each 225 Ah battery I installed weighs 70 pounds. All together, my battery bank weighs roughly 280 pounds. To support that weight in my storage bin, I built and installed a steel support bracket (see photo below) that bolts directly to the frame of the RV. So keep the weight in mind when choosing the location for your battery bank.

Fri, 06/09/2017 - 06:59 - 4 six volt batteries installed in battery compartmentFlickr

Fri, 05/26/2017 - 20:49 - Battery compartment support bracketFlickr

Cable Thickness and Length

Keep in mind that when wiring batteries together, you are essentially creating a very large battery. You want the energy to flow freely between each battery across the cable connections with little to no resistance. This is why we use very thick cable for this. In the video I used #1/0 gauge cable.

It is also a good idea to keep your interconnecting cables the same length. Use the shortest cables possible. Doing so creates an even and efficient flow of energy across all batteries which ultimately aids in charging and overall battery efficiency.

If you have any question, comments or suggestions, please leave them below and I’ll do what I can to answer or point you in the right direction.

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