Tuesday, November 28, 2023


Ask Dave: How should the RV’s 6-volt and 12-volt batteries be wired?

Dear Dave,
I have a Class A diesel pusher motorhome with two 6-volt and two 12-volt batteries. How should these batteries be wired? Any info on this would be appreciated. —Carla, 1999 Overland Lorado

Dear Carla,
Without seeing firsthand the types of batteries and the configuration, I have a couple questions. We will probably make some assumptions.

First, what type of batteries are the two 12-volt batteries? Since it’s a diesel pusher, I would assume those batteries are automotive “cold cranking” batteries that are used to start the engine. It’s not uncommon for Class A RV manufacturers to put both the house and engine batteries in the same compartment. These would be connected parallel with the positive to positive and negative to negative.

6-volt batteries

The two 6-volt batteries typically would be deep cycle batteries that are designed to hold a deep charge and power the house functions and recharge known as “cycles”. Since they are 6-volt, they need to be connected in series, which means positive to negative, which creates a 12-volt power supply.

Here is a setup similar to yours on a 2015 Thor we recently worked on:

It’s hard to see due to the rat’s nest of cables and wires. However, there is a cable looped in the back that jumps the positive to negative. These batteries have been extremely neglected as the terminals are corroded and the batteries themselves are swollen. These are not original batteries. I believe the unit came from the factory with four 6-volt batteries, as the tray shows a space for two more.

Don’t mix RV’s 6-volt and 12-volt batteries

Another question I have—or, more important, a concern—are the two 12-volt batteries connected to the two 6-volt batteries? I have witnessed units that had batteries added and since they could not find 6-volt batteries, they added 12 volt. They mixed them, thinking that since the two 6-volt batteries created a 12-volt bank, it would work. You do not want to mix 6-volt batteries in series with 12-volt batteries. They have different chemistries and will not work well together.

Make sure you have the same brand and type batteries in the house application, and do not mix 6-volt with 12-volt.

Dave Solberg is a leading expert in the RV industry and the author of the “RV Handbook.”

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Dave Solberg
Dave Solberghttp://www.rv-seminars.com/
Dave Solberg is a leading expert in the RV industry and author of the “RV Handbook” as well as the Managing Editor of the RV Repair Club. He has been in the RV Industry since 1983 and conducts over 15 seminars at RV shows throughout the country.



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Thomas D (@guest_190018)
1 year ago

Sometimes it would be best to say” I’m sorry, I’d have to make too many assumptions. If wrong you let the smoke out of starter motor,alternator, voltage regulator the wires themselves. My boss has a dump truck with 24 volt starter. Whats the wiring for that?

Don (@guest_190002)
1 year ago

No argument, Dave. But one minor error: the chemistry of 6v and 12v lead-acid batteries are identical. The structure is different between deep-cycle and starting batteries, and you’re totally correct about not mixing them, ever. But I’m afraid you flunk chemistry on this quiz…

Joe (@guest_190057)
1 year ago
Reply to  Don

I agree with lead acid batteries the chemistry would be the same. What I would not do is mix deep cycle and cranking batteries together as they could have different discharge and charging rates. That being said there are 6 volt starting batteries out there for the antique car purest that does not want to convert his vehicle over to 12 volt.

Tom (@guest_189976)
1 year ago

If you are installing pairs, regardless 6 or 12 volt, try to also match build dates. As close to similar you can get, the better.

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