Saturday, December 3, 2022


RVelectricity – Just Ask Mike (J.A.M.): How dry I am – Don’t let your RV battery explode!


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,
These pictures just came in from one of my Facebook Group members. Yes, it is indeed as bad as it looks.

A battery explosion

It appears that the multi-stage charger might have failed and kept pumping significant current into the batteries, after it should have gone into “float” mode. The poster noted that he only had to add water every 6 months, so he consequently only checked water level every 6 months.

This was compounded by how far he was away from the RV, so it would often sit for 6 months by itself while plugged into power to keep the batteries fully topped off.

Batteries are potential bombs

So, all was well until apparently something happened with the multi-stage charger that caused the water to boil out the batteries, one of which exploded. When the water boils out of a lead-acid battery and exposes the plates, there can be serious outgassing of hydrogen and oxygen gases in the perfect ratio for an explosion.

If these gases accumulate in the top of the battery due to a void from a lack of water, then it only takes a spark from one of the overheated plates to make a small bomb. And it’s powerful enough to blow up the casing of the battery and spray sulfuric acid over everything in the area. Then you have some serious cleanup to do in addition to replacing the batteries.

What to do?

First of all, never leave your battery plugged into a standard trickle charger or old-school RV charger. That’s just asking for overcharging trouble. Also, I highly recommend monthly checks of the electrolyte level in your FLA (Flooded Lead Acid) batteries. While it may not be convenient to do this in some RVs where the batteries are located in a hard-to-reach location (like under the steps), nonetheless, checking the electrolyte level monthly is very important. Don’t become my next poster child for battery explosions.

Making it easier with Flow-Rite

I haven’t completed my review of the Flow-Rite battery watering system just yet, but I’ve had a number of unsolicited testimonials from readers who have used the Flow-Rite system for years with great success. They note that it only takes two minutes to check the electrolyte level on up to four batteries at the same time, and fill them with distilled water. Best of all, you don’t even have to touch the batteries to check the level. There’s just one place to fill and you’re done. Seems like the real deal to me – which is why I asked for a review sample from Flow-Rite Controls™, Ltd. As soon as it warms up a bit I can complete my review. Brrrrrrr!!!!!

Charging options

If I needed to leave an RV unattended for 6 months at a time, I would consider shutting off all shore power to the RV and hooking up a Battery Tender instead of the on-board multi-stage battery charger.

Battery Tender has a great reputation for making a product that floats your FLA or AGM batteries perfectly. And you can even get solar versions in case you need to store your RV in a spot without electric power, but that does have sunlight. Just remember that Lithium batteries don’t need (or want) to be float charged in most cases. But check with your battery manufacturer just to be sure.

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 For more info on Mike’s qualifications as an electrical expert, click here.
Join Mike’s popular and informative Facebook group.
And you don’t want to miss Mike’s webcasts on his YouTube channel.

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Jim Johnson
26 days ago

When I store our camper in a location without AC power, I disconnect the AGM deep cycle battery from the camper (switch on ground side) and plug in my POWOXI Solar Panel, 12V 10W Magnetic Solar Battery Charger Maintainer. I modified my battery box to include a SAE Quick Connect, so setup is really fast. I have a solid year’s (over a couple years) use and it works like a champ, even when not directly aimed at the sun.
Note: that quick connect is fully bidirectional. I can use it to power a macerator/pump for black tank emptying and I have a quick connect to 12v automotive jack adapter to run a 12v compressor (camper tires are only 60 psi). Make sure you are properly fused. No the solar panel isn’t going to quickly recharge the battery after using these high-demand devices, but when I use them I am typically I’m either hitched to a tow vehicle or on shore power to handle that.

26 days ago

Can I use one battery tender for more than one battery?

Mike Sokol
26 days ago
Reply to  Greg

Yes, just connect it across the main negative and positive terminals. So it works with a pair if 12-volt batteries in parallel, or two 6-volt batteries in series, or even four 6-volt batteries in series/parallel.

1 year ago

(novice here) So if I upgrade my (2) 6-volt wet cell batteries to LiFePo, then do I need to also upgrade my 13 yr old converter/charger to a multi stage converter/charger that supports LiFePo? Does the charging voltage from the alternator on my MH flow thru the converter/charger as it charges the house batteries?

Montgomery Bonner
1 year ago

I keep saying some people are just too ignorant to own RV/BOAT/Car. They are used to batteries which need no maintenance. All RV’s come with the cheapest batteries possible, UNLESS you upgrade to AGM/Lithium-Iron type, Those are sealed, and DO not need checking. I check my lead acid ones about every two to three weeks, sometimes one or two cells need water. But give me a break, every 5 months is just stupid.

David Telenko
1 year ago

Greetings Mike, your article today was very informative but scary to say the least! I do have a question in regard to gases accumulation in a void at the top of the battery & it would only take a spark from one of the overheated plates to make it explode! So how would a spark happen in the battery, I could understand a possible spark happening with a solenoid or relay or maybe a loose connection, or even worse if the owner opened the access door & a light came on causing a spark!
Just to let you know you have SPARKED my curiosity!!

Mike Sokol
1 year ago
Reply to  David Telenko

Plates can warp when they overheat. If the insulation breaks down they can make contact and creaet a spark. Then it’s boom boom time…

Thomas D
1 year ago

When returning to my winter home in AZ I checked my golf car batteries and found them dry. I had purchased an expensive battery maintainer to prevent a thing like that happening. I added 4& a 1/2 gallons of distilled water and charged it back uo. All seems to be good and specific gravity is pretty good considering.
I called the company that made the maintainer and was told ” if any of the cells are bad or weak the maintainer will try to bring them uo to full charge and could boil out the other cells.”They said ” buy a timer and charge just an hour a day”. My cart is 48 volts with 6- 8 volt batteries. 24 cells.

Richard McLaughlin
1 year ago

Hi Mike,
Love your articles and lessons. Regarding the Flow-Rite system, there have been similar systems for filling multiple batteries in golf carts. There have also been several reports of multiple batteries exploding due to the hydrogen being shared through the filling tubes.
Thanks, Rick

1 year ago

Another excellent article Mike! Could you also speak to the temperature range a wet cell battery can endure? For example, at what point do we need to worry about a fully charged wet cell battery, maintained by a Tender, freezing? We’ve had some record cold temperatures here lately.

Tommy Molnar
1 year ago
Reply to  Ray

My understanding is that fully charged batteries won’t freeze. Not sure about 30-40 below zero, but I’ve had my six volt batteries sit outside when it was a few degrees below zero (fully charged with my multi-stage converter) with no ill effects.

Mike Sokol
1 year ago
Reply to  Tommy Molnar

More to study and write about. Yippie!!!

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