Saturday, May 27, 2023


Ask 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)

Dear Brian,
According to the brochure I could find online, your Leisure Travel Van came standard with two 6-volt deep cycle batteries and a standard converter that is 70 amps. If you have the original batteries still in the vehicle they would be more than five years old at this point. If that’s true, I would guess you are not getting even 50% amp hours out of them. The brochure did not list what group (24, 27, 31) or amp hours were installed and you did not list what batteries are in the rig now or the solar panel wattage.

Here is a set of 6-volt batteries that are only three years old and you can see they are so sulfated they don’t hold a charge at all. Even if your batteries are not this bad, 6-volt batteries are connected in series, which means positive to negative, which gives you a 12-volt bank but does not double the amp hours. These were very cheap group 24 batteries with 105 amp hours. With lead-acid batteries you can only draw them down 50%, so that means 50 amp hours when the batteries were operating at full capacity. So if you have two 6-volt batteries connected in series, that would mean 105 amp x 12 volts, which gives you 1260 watt-hours. You can only use 50%, so that means 630 watt-hours.

RV solar calculator from Go Power!

Go Power! has a great information page that helps identify the components you use in the RV and what that means for the power you will draw. You can view it here.

There is no perfect science as it is hard to calculate how many hours you will have components running like the lights, water pump, furnace and other items. But it is a good exercise in getting close to what you might need for power. The brochure also indicates you have a 3-way refrigerator. So if you are using the 12-volt mode through an inverter, that will draw more than most of the other components combined.

Solar panel charging

So why don’t the solar panels keep the batteries charged up? According to electrical expert Mike Sokol, the average 100-watt solar panel will be able to provide 300-400 watt hours per day. And that is in perfect conditions with direct sunlight. Read his article about that here.

With everything off in your rig, those two panels will only be able to provide 600-800 watt-hours per day. I would imagine your calculations showed somewhere between 750-1000 watt-hours per day, so your 200-watt panels can’t keep up.

solar panels on an RV's roof

Running the engine does not charge them

The alternator in your tow vehicle will only put out about 14 volts to charge the engine battery and the house battery through the 7-pin connector. As stated earlier, it will take more than six hours with the solar charging system, so 15 minutes will do very little to charge the batteries.

 You might also enjoy this from Dave 

Part 1: What is the best solar panel for my RV and how many do I need?

Read part 1 in Dave’s series here.

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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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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7 months ago

High quality solar panels degrade and lose about 0.5-3% per year of output. It is depending on air temperature, thermal cycling, damp heat, humidity, freezing and UV exposure which degrades them faster, cheaper panels can lose even more. If you figure a middle of the road quality panel he probably lost 5-8% +/- of output since 2017. Combine that with 5 year old batteries even if they are well maintained, he has lost of a lot of function.

Left Coast Geek
7 months ago

if they are 2 x 6V batteries, they are almost certainly GC2 deep cycle golf cart batteries. those are 210-225AH usually. Group 27, 31, etc in an RV are 12V marine/rv batteries which are not true deep cycle.

Tommy Molnar
7 months ago

He stated he had a 2017 Leisure Travel Van (Unity), not a trailer, but I don’t think that much matters in the scheme of things.

Bob p
7 months ago
Reply to  Tommy Molnar

That part of the answer may have came from Johnny Robot. Lol

7 months ago
Reply to  Tommy Molnar

I’m thinking Dave put that in there just in case other RV’s were having the same issue, like trailers! Though i was wondering how Dave could tell from the picture that those batteries were sulfated, they look very un-maintained!

7 months ago
Reply to  Snoopy

That’s a stock picture of scary looking batteries they’ve used before as an example.

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