Thursday, December 8, 2022


RV Electricity – Just Ask Mike (J.A.M.): Solar battery tender?


By Mike Sokol

Welcome to my J.A.M. (Just Ask Mike) Session, a weekly column where I answer your basic electrical questions. If you’re a newbie who’s never plugged in a shore power cord (or ask – what’s a shore power cord?), or wonder why your daughter’s hair dryer keeps tripping the circuit breaker, this column is for you. Send your questions to Mike Sokol at mike (at) with the subject line – JAM.

Dear Readers,
Once again the question has come up on my Facebook group about how to maintain the health of RV house batteries when the RV is parked somewhere remote without a nearby electrical outlet. Of course, you can get a solar panel and a separate charge controller, then add some kind of float charger (such as a battery tender, etc.). But that’s a lot of work and expense if you just need a battery tender and a solar panel.

Well, look what I just found – a 15-watt trickle/float battery tender with a built-in solar panel. It’s waterproof so you can mount this solar panel with an integrated float charger however you like on the outside of your RV so it gets lots of sunshine. According to the literature, it will properly float-charge flooded cell, AGM or lithium batteries, and will work with a single 12-volt battery, two 12-volt batteries in parallel, and two or four 6-volt batteries in series or series-parallel.

And if this is a temporary storage situation, simply route the connecting cables through whatever access hole you can find into your battery compartment, using the supplied alligator clips to connect it to the RV house batteries. Now all you have to do is turn the RV battery connect switch to the OFF position in order to reduce parasitic drain, and your RV batteries should be safely maintained by the sun for months on end without fear of damage. Sure is a lot easier than disconnecting and carrying all those heavy batteries into your garage to put them on a float charger.

OK, everyone. Remember that electricity is a useful and powerful force, so we all need to pay attention to safety precautions while using it.

Let’s play safe out there….



Mike Sokol is an electrical and professional sound expert with 50+ years in the industry. His excellent book RV Electrical Safety is available at ##RVDT 1327;##RVT946

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2 years ago

I see the panel truly is a Deltran Battery Tender. Although often used as a generic name, Battery Tender is a registered trademark by Deltran. Anyone shopping needs to be sure to get the real thing rather than a cheap imitation.

2 years ago

“15-watt trickle/float battery tender with a built-in solar panel” sounds like exactly what I need to keep my house batteries (two 12V in parallel) from dying while in storage. I live in the north and the specs say this is good from 120 F. to minus 20 F. It does get colder than that occasionally but doesn’t usually last longer than 7 consecutive days so I don’t see that as problematic.

In reading the Q and A on the Amazon site I am wondering if this wouldn’t work for my RV:
The question was can you use it on two 12V batteries in parallel
The answer was no, you have to disconnect the batteries from each other

Mike, your write-up stated it would work on two 12V batteries in parallel.


Larry H Lee
2 years ago

15 watts translates to a bit over 1 amp at 12 volts. That would be an average of 5 AHr/sunny day. I doubt that would be sufficient to maintain 4 golfcart batteries plus whatever residual parasitic loads remain despite switching the batteries to “storage”.
Just my opinion based on storing our 40′ Thor class A diesel pusher with 6 each 12 volt AGM batteries and 2 each 100 watt solar panels in Virginia where it does get cloudy often.

John R Crawford
2 years ago
Reply to  Mike Sokol

Thanks for the offer Mike but since I’m full time I don’t think I can isolate my batteries and still live in the coach.

2 years ago
Reply to  Mike Sokol

Different rigs have different parasitic loads, Mike. My Country Coach (2x8D house batteries) will draw down those batteries to flat dead, even with the “salesman switch” off, in a couple of weeks. Learned this the hard way, obviously, so I have made sure never to leave it un-powered for more than a few days. I haven’t calculated the draw down rate, but I’m pretty sure it’s way more than 15 watts.

John R Crawford
2 years ago

Mike, I am Full-timing In a 35ft diesel pusher and would love to have something like this to keep from running my generator as often when boondocking. I know this trickle charger won’t keep up with the usage but would it keep me from having to use my generator as often. We never store our RV.

Donald N Wright
2 years ago

I am on my second “battery Tender”, when I purchased a larger battery, the smallest unit would no longer keep it charged.As I have an Aliner popup trailer, it is wired directly to the battery.As my electrical power usage is minimal, the battery tender keeps everything charged for stays in National Parks. No smoky, noisy generators for me!