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.
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
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.
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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