Tuesday, October 26, 2021

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RVelectricity™ – Just Ask Mike (J.A.M.): Lithium battery winter storage

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) noshockzone.org with the subject line – JAM. This week I discuss lithium battery winter storage.


Dear Mike,

I’m getting ready to put my RV in storage for the winter again. Last year I left my original lead-acid battery out in the RV (and the cold) and by springtime it was dead and wouldn’t hold a charge. I did upgrade to the lithium battery and new controller/charger, and it’s been working great. What do I have to do to protect my new lithium battery investment this winter? Should I bring it inside? How about some sort of trickle charger? I have a battery disconnect switch, but is that enough? —Frank P

Dear Frank,
Actually, now that you have a lithium battery, winter storage is easier than you might think. While standard lead-acid (flooded lead acid, or FLA for short) batteries self-discharge fairly rapidly, sometimes as much as 10% to 20% per month, the modern crop of lithium iron phosphate (lithium for short) batteries tend to self-discharge around 1% to 2% State of Charge (SoC) per month.

Lead-acid (and AGM) batteries need a battery maintainer

I don’t recommend that you bring your lead-acid batteries (both FLA and AGM) in from your RV unless it’s to keep them from being stolen. That’s because in the springtime I’ll get a ton of emails from readers who pulled out their batteries, and when they reconnected them in the spring they hooked something up backwards. That’s a recipe for (at the very least) blowing the fuses in your inverter and other DC appliances. In the worst case, it can do serious damage to your 12-volt DC appliances.

So don’t take batteries out of your RV (unless you really have to), but do remember to turn off the battery disconnect switch in your trailer.

You’ll also want to do one last check of your water level in an FLA battery and top it off with distilled water if necessary. Of course, if you have an AGM battery there’s no water/acid level to check.

Watch out for self-discharging batteries

However, lead-acid batteries (be they FLA or AGM) will still self-discharge over the winter months without some sort of maintenance charger. I really like the basic Battery Tender units like this one. All you have to do is clip it onto the negative and positive battery terminals, plug it into a source of 120-volts AC, and “Bob’s your uncle.” It really is that easy.

Don’t trickle charge it…

And don’t use a trickle charger or whatever vintage 2-stage charger you may have in your older RV over the winter. Nope, they will do the opposite of allowing your battery to self-discharge. It will over-charge it and boil out the sulfuric acid from the battery, corroding and destroying everything it touches.

Sometimes the batteries just swell up like this one and sometimes the acid just bubbles out of the vent holes. And I’ve actually seen the sulfuric battery acid rot out the metal floor of the battery compartment of an RV. It ain’t pretty, in any event.

Lithium batteries don’t need nothin’ over -4F

Many of the lithium battery manufacturers recommend simply charging them up to between 50% and 100%, disconnecting them from your RV electrical system via the battery ON/OFF switch, and leaving them alone. And many Lithium manufacturers don’t recommend using a maintenance charger in storage, but some will allow it. Guess it depends on their internal battery charge controller.

I did this last winter with my lithium test battery and lost less than 10% of charge over 6 months in cold storage. Unlike the rest of us, a lithium battery is happy out in the cold down to -4 degrees F. Of course, they need to be warmed up before charging them, but during normal winter cold they are just fine sitting there.

Check with your particular battery manufacturer, but this seems to be the proper procedure for lithium batteries. Some say charge to 100% SoC, and others say only charge them to 50% SoC. And some recommend storage no lower than -4 degrees F. So, follow your particular battery manufacturer’s recommendations and you’ll be fine. Of course, there’s no sulfuric acid in a lithium battery to leak out, and no water levels to maintain. It’s a beautiful (and no maintenance) thing. Just remember to turn off your battery disconnect switch and you’re in business.

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 Amazon.com. For more info on Mike’s qualifications as an electrical expert, click here.
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And you don’t want to miss Mike’s webcasts on his YouTube channel.

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Wayne
23 days ago

I have left the acid batteries in our kids fifth and am leaving it plugged in. This has been a trailer we find hard to seal up and keep the mice and chipmunks out of.
I have discovered that if I leave the radio tuned loudly to a “Country” FM station…no more chipmunks and mice!!
Never tried a “rap” station😜

wolfe
24 days ago

Lithium batteries are FINE being discharged below 0*F… you may get less amperage at super-cold temps, but that’s usually not an issue until you have a beefy inverter.

What is NOT AT ALL FINE is charging them below 0*F, where they will quickly grow metal dendrites through the insulator, which will destroy the battery (potentially dangerously so). NEVER charge a lithium battery below 0*F, no matter what even the manufacturers claim. NEVER NEVER. Yes, I know some batteries have heaters, but they don’t heat evenly throughout the mass, so unless the battery is honest-to-gawd in your heated cabin (not storage), NEVER NEVER. Hopefully I’m being clear there?

wolfe
24 days ago
Reply to  wolfe

As for SoC, you want to store any lithium battery “ideally” at about 60%… however, it doesn’t really matter because you’re talking “1000 charge cycles vs. 1200 charge cycles” type math. Don’t discharge “artificially” to that point, because that’s another charge cycle, which “costs” more lifetime than just leaving them nearly full charge.

Never discharge to 0 SoC (yes, that does hurt them).

Never leave it on a trickle charger if you’re not drawing ANY power from it (usually because you disconnected it). Most chargers “check” for needing a charge by applying a small charge, and some can ultimately overcharge just by the checking.

So, although I explained more of the WHY it is pretty correct saying to just disconnect it and leave it alone until Spring.

Thomas D
24 days ago

Here in Wisconsin it gets a LOT colder than -4 degrees..so, take the batteries out, right? And as far as battery maintainer, I bought a very expensive one for my golf cart. Boiled all the water out of 24 cells. I was told because there may have been even one bad cell the maintainer will try to bring it up to full charge. Thereby over charging the other cells. I now use a timer and charge an hour or so a day. No problems. As far as lithium, they are a lot lighter so if damage can occur wouldn’t it be wiser to take them out. Mark where the wires go and also take a picture. Everyone has a camera these days.

wolfe
24 days ago
Reply to  Thomas D

I take my lead batteries inside, because they can freeze at Canadian temperatures even if they ARE charged. I’ve had batteries freeze ON the charger in my protected-not-heated garage when it was -20 outside.

I leave out my Lithium batteries, per the above long post — they aren’t being charged or discharged, and don’t mind the cold while doing neither.

Tommy Molnar
27 days ago

When I went from golf cart batts to Li On I was told to install a ‘shut off switch’ between my solar panels and the controller so when it got REALLY cold my controller would not continue to try to charge my new batteries. They can sit forever (well, almost) with no harm as long as I don’t try to charge them in sub-zero temps. They can be discharged (as in being used) in the cold but not charged (until the temperature goes up). And, these batteries are installed in the storage area instead of outside like the old batteries.

Michael Gray
28 days ago

I have a Lithium Iron starter battery on my motorcycle. It was designed as a “drop-in” replacement for the SLA, and has so far been doing well. I’ve found that it needs little to no maintenance at any time of year, just as you said. Only time it needs charging is if I did a dumb thing like leave a cell phone charger plugged in (they draw phantom power even when not in use). I have a battery tender made specifically for Lithium for when I make those kinds of mistakes. But I’ve had it for 5 years now, and it still works perfect.

It has one quirk though. When the temperature is down in the 30’s F, It needs to warm up a bit before it can produce enough amps to turn the engine over. Keeping the headlight on for a couple minutes is usually enough. My particular manufacturer recommends that, though not all batteries will be “self-warming” like that.

Not exactly RV related, but I thought folks might like to hear from someone who has been using one of these batteries for a while. 🙂

Drew
29 days ago

We have 2 rv’s in the family. Sometimes we go for a couple of months without camping. I just have disconnects on both. The batteries hold enough charge to start generators and use lights/water pumps when we’re ready to go again. I’ve never had to use any maintainers/chargers while the rigs stayed idle.

Brad Teubner
29 days ago

Info on my CALB cells say they should not be stored below -20C (-4F).
Relion specs say the same.
Also, some Lithiums have internal heaters for cold weather use, and that could possibly cause some deep discharge.

Tom H.
29 days ago

Mike, I just installed 200 watts of solar on the roof. I assume that I would Not disconnect my lithium battery, and just let the solar panels do their thing. Is that correct?

Mike P
29 days ago

Will lead acid batteries/6V golf cart batteries freeze and break in cold climates (ie Erie, PA)?

Crowman
29 days ago
Reply to  Mike P

Same rules apply to 6 volt as 12 volt.

Roger V
29 days ago

AGM to Battleborn lithium Coach batteries – best upgrade ever!

Ed K
29 days ago

Unfortunately, my Battery disconnect switches do not disconnect all loads in my Motor Home so if I want to fully isolate my battery banks, i need to remove all the Negative Wires and Cables from both sets of batteries.

Bob P
29 days ago

Mike don’t you think the same people who might hook up the battery cables with reverse polarity when they reinstall their battery from winter storage would have trouble connecting a battery tender with the correct polarity. To quote Ron White, “you can’t fix stupid”. Lol

tom
29 days ago

excellent as usual. How about a short item on converting to Li battery, as least for storage compartment.

tom
24 days ago
Reply to  tom

Second vote on conversion.