Wednesday, March 29, 2023


What is the best battery setup for boondocking?

Dear Dave,
Can you help draw up a new house battery system for me. I want to do a lot of boondocking, and don’t want to run the gen set a lot to recharge. My house charger is pitiful—undersized. And I’d like to also install PV panels on the roof. I have four 6-volt Trojan deep-cycle batteries, which went south this year and won’t take a charge. Would appreciate all you could do for this disabled veteran. Thank you. Semper Fi. —Bruce, 2015 32-foot Precept Jayco Class A

Dear Bruce,
First, thank you for your service.

The four 6-volt Trojan batteries would have been good at the start “IF” they had been maintained properly, which means a multistage charger to break up sulfation. I’m sure your Class A does not have that, but rather a simple WFCO that charges 13.6 volts until the batteries reach 12.6 volts then drops to a maintenance or float charge of 13.2 volts.

First step

The first step in designing the best system for you for boondocking is calculating what amp hours you believe you will need, then how to factor in the batteries and if you want or need to go with solar panels. Go Power! has a very good worksheet that gets you started in determining what 12-volt components you think you’ll use and for how long.

The big items are furnace and a residential refrigerator. From what I see in used RV photos and video walkarounds, it looks like you have the 4-door Norcold absorption refrigerator. That would run on propane and draw a little 12-volt power for the control board and thermistor.

As I have stated many times, there is no exact science to calculating how much battery power or amp hours are best for you since everyone RVs a little differently, but this is a good start. Another good source of information is the Go Power! sheet on typical battery and solar panel sizes for units.

They recommend a Class A unit like yours would need 400 Ah AGM battery power for a 1- to 3-day boondocking trip. That would provide 200 Ah of power, since you should only drain them down 50%. That typically means four batteries connected parallel, which is positive to positive, negative to negative. As you can see, going with lithium would mean only two batteries at 100 Ah each for that same 200 Ah of power. If you are planning to go longer, it means a much larger bank. I would recommend the two lithium batteries, as they will more than pay for themselves in the 10-year warranty. Make sure you read the article on installing lithium and finding a quality battery company here.

Next step

Next we need to spec a converter/charger, as yours will not charge either type of battery sufficiently. I would recommend the Progressive Dynamics converter designed for either type of battery such as the PD9100 we installed in the 2015 Thor Challenger. Most lithium batteries require 14.6 volts to charge them to 100%. This is a very cost-effective converter and easy to install.

If you need to run some 120-volt appliances such as the TV, outlets for CPAP or charging phones and such, then you can go with a smaller 1000-watt inverter but need to factor in the draw from that. Another option is to go with a larger inverter/charger that will not only power the 120-volt items you want, but will also charge the batteries to full capacity. In this case I would suggest the Go Power! 2000-watt model.

There are several others on the market that will work. You just need to be able to customize the charge for the voltage and the length of charge.

Final step

The final step is to decide if you want solar panels, what size you need, and where to install them. If you go with the two 100 Ah lithium batteries, you can see by the chart that the best solar panel for that situation would be 380 watts for a short boondocking trip and 570 watts for extended stays. Once again, this is not exact science. You can always start a little smaller and add to it if needed. You might be able to supplement the charging by using the generator slightly.

Most people stick three or four panels up on the roof. However, keep in mind that you need to be in direct sunlight for the system to provide a charge. Since you are boondocking, you don’t have 120-volt power for the roof air, so that means the inside of the rig will heat up 20–30 degrees. I am a big fan of the portable units so you can be cool in the shade and still get the benefit of solar charging.

This will take more panels and more time to set up and tear down, so that is another consideration. You can see there are several options and no perfect solution that fits everyone. Hope this helps get you started in calculating the power you need.

 You might also enjoy this from Dave 

Why aren’t my solar panels charging the house batteries?

Dear Dave,
I have solar panels to help charge the house batteries while boondocking, but after a couple of days the house batteries are dying. I turn on the engine to recharge the house batteries, but often it won’t charge them, even if I let the engine run for 15 minutes or more. Sometimes it charges as soon as I start the engine. What’s going on? —Brian, 2017 Leisure Travel Van (Unity)

Read Dave’s answer.

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

Read more from Dave here


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1 month ago

Don’t have to swap out the entire converter. I upgraded my WFCO with a replacement board to charge two battleborn lithium batteries 380watts solar with a victron MPPT solar controller in our class C sprinter. Have spent a week off grid with no problems. Also might want to look into a dc to dc charger..

Neal Davis
1 month ago

Interesting stuff. Thanks, Dave. I am gathering information with the idea of adding solar panels and replacing AGM batteries with lithium rather than AGM when the time comes. Thanks again!

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