Thursday, September 28, 2023


Will RV’s house batteries ‘play nice together’ if I replace chassis battery with lithium?

Dear Dave,
It’s just about time for a new battery in the truck portion of my motorhome. I’ve been thinking of upgrading to lithium. I added a second house battery wired in parallel about two years ago when I replaced the factory battery. They are both in great shape. Question is: Is it OK to have a lithium truck battery and regular house batteries? Will they play nice together? —Judith, 2018 Coachmen Freelander Micro

Dear Judith,
I would not recommend installing a lithium battery for your “truck” battery. I believe your Coachmen Freelander is on a Ford E Series Chassis, either a E-350 or E-450, and has deep- cycle batteries for the house batteries, as you have indicated. If they are wired in parallel, they are 12-volt deep cycle and it is good that you had two new deep cycle batteries installed at the same time and did not just add a new one. If you just add a new battery, the old one will draw down the new one and you will not be able to charge and drain them as designed.

This is a photo of two house batteries in an older Coachmen Freelander that I used for several videos. They are located under the steps and the chassis battery is in the engine compartment. The truck, or chassis, battery is a cold cranking amp (CCA) designation. That means it has initial high amps to turn the engine over and start and then is kept at a constant state of charge through the alternator. The deep-cycle batteries are designed to be drawn down 50% and recharged by a converter or solar panels, but can also be charged by the engine alternator while driving.

Will they play nice together?

The chassis battery and the house batteries really don’t interact with each other unless the momentary switch is engaged. Your rig has what is called a Battery Isolation Management (BIM) solenoid that is designed to be installed in between the two batteries. The house batteries provide 12-volt power to the distribution center, which powers your 12-volt components through automotive-style fuses.

If the engine is running, the engine alternator provides a charge to the engine battery and to the BIM. That allows the charge to go to the house batteries to charge them while driving. If the engine battery goes dead, there is typically a momentary switch that, when pressed, provides a jump start to the house batteries. This is the only time the two batteries really interact—it’s just for a jump. I do not believe there would be any issue if you used a lithium battery for the chassis, as the house batteries would simply provide a 12-volt assist or jump.

Why not lithium?

Most lithium batteries that I have come across are deep-cycle batteries and are designed to provide a steady 12-volt power supply and not an initial high-cranking power supply. Most of the companies that I deal with have stated they are not even designed to turn over the generator when used in a house battery situation. Check out the article here.

Some companies said they were not designed to have enough CCA, while others said they did. Confusing, at best. However, the companies that I have worked with use the UL-approved cells and stated they did not recommend their batteries for turning over the generator. So I would believe that would be the same for the engine.

The main reason I would not use a lithium battery for the chassis is that a good lithium battery will run around $800-$1000. That would be a waste of money for something that is just designed to start the engine. A typical CCA engine battery for a smaller vehicle like yours would run approximately $150, if not less. So, even if the lithium battery has the ability to turn the engine over, I would not waste the money.

 You might also enjoy this from Dave 

Comparing pricey lithium batteries to cheaper ones: How to differentiate quality

Just a year ago you could hardly find a lithium battery for under $1,200, but now I see them advertised all over the place from $1,200 down to some that are $350 for a 100 AH model. So what’s the difference in cost of lithium batteries? I realize that first-generation products have a higher price to cover initial engineering costs, like the $600 VCR that became $99. But why do we see such a current range in prices? What makes some more expensive, and is the price worth it?

I spent quite a bit of time the past couple of years researching the different lithium battery offerings, charging systems, and installation issues. In this short series, I’ll teach you what I’ve learned.

Continue reading.

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

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Dave Solberg
Dave Solberg
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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25 days ago

Hey Dave – great articles!

There’s nothing more reliable than a good deep cycle AGM Battery on boats and RV’s.

Tires and batteries – two most important items needing reliability, and I replace them regularly (boat, house genset, RV, F250 truck and car).

I think an educational article on lithium battery fire safety could be important and a great topic to recommend for future.

Keep up the great work!

Bill Byerly
29 days ago

Good to know Dave, thanks. Probably even save a few $$ for someone in the future!

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