Tech Tips: Battery Storage Wives’ Tales

If you go outside with wet hair, you’ll catch your death of cold!” So said Grandma. She was also very big on, “If you want to see well at night, eat lots of carrots!” And for every kid who rolled and crossed his eyes when hearing one of Granny’s maxims, there was always the big scare: “Cross your eyes like that and they’ll stay that way!” 

Grandma had a million of them. But Grampa wasn’t too far behind—maybe it was their close association with one another.  One of Grampa’s stories that we hear with remarkable frequency, even in this  “enlightened” age, was this one:  “Don’t set your battery on concrete—it’ll go dead in no time!  Always leave it standing on boards!” 

Will batteries run down if left on concrete?While Grampa has long been on “layaway,” the old stories persist. It was hard for me to believe, but we recently had a disconcerting discussion with a heavy equipment mechanic.  With a straight face he told us that one should never store a battery on concrete because that act would run the battery down. Mind you, the fellow is in his 40s. I dare say I found it hard to resist asking him if he believes in the existence of the tooth fairy. Where did this humdinger of a story come from, and really, how best do you store a battery that’s not in service?

Well, laddy, let’s go back in the dark ages together. No, you don’t need to conjure up visions of Benny Franklin and his shocking experience of flying a kite in a lightning storm, but it does go back a ways.  Sometime in ancient history, early batteries had wooden outer cases; inside were glass jars, making up the inner battery cells. Set the battery box down on concrete—or onto a damp earthen floor for that matter—and it was a simple matter for the wood case to pick up moisture. As the wood swelled from the moisture, it wasn’t a far stretch to see how the glass containments might become pinched and broken. 

Later, the wood boxes gave way to early rubber battery cases. This rubber is not like rubber we are acquainted with today—it had a fairly high content of carbon, an electrical conductor.  The theory went that the carbon acted as a conductor, allowing the flow of electrons, hence discharging the battery.  I’m still not sure how this was all supposed to work, unless perhaps that juice flowed from one battery terminal to the other due to moisture on the surface of the case allowing such.  Of course, put it on the floor, or put it on a bench, seems to me that you could still have this disastrous flow.

Problem Solved
Today battery cases are generally high quality, non-electrically conducting plastic.  There are no fears of “glass cells” inside your battery case getting pinched in any fashion, so the fear of leaving a battery on a floor—concrete or otherwise—is simply a non-issue. 

Fear of floors aside, there are still considerations for storing your batteries during a period of non-use.  First, an RV battery (or starting battery) will “self-discharge” over time.  This can actually amount to a fair amount of loss—think in terms of almost 4 percent of the battery’s capacity over a month. You may be able to let your RV take care of its own batteries, keeping them up-to-snuff and handling the self-discharge problem.  Much depends on what sort of equipment your RV comes with. For most of our family RVs, we’re still back in the so-called dark ages where our factory-equipped battery converters are old-style noisy transformer jobs.  Sure, when we plug our rig into shore power, there is low voltage available for operating lighting circuits, and theory has it that the house batteries are being “charged” by this lash-up. Nevertheless, we don’t have a lot of confidence in these old-school converters, and so for long periods of non-use, we chose other methods of keeping our batteries up. 

On the other hand, your RV may come with a “smart charger” system built in. An intelligent charger system reads the state of the battery, and then applies the correct amount of charge voltage and current to bring it up to full charge, and then “floats” the battery at the optimal voltage.  A smart charger system will not over- or under-charge your batteries.  If you don’t have a smart charger and are concerned that the battery left in the rig could somehow be a liability, what’s to be done?

Charging Ahead
First, make sure the battery is clean. Don’t allow a layer of dirt or crud to accumulate across the top. Sure enough, dirt is an electrical conductor, and small amounts of juice (in addition to the self-discharge issue) can steadily chew away at your battery’s charge integrity.  A damp cloth will clean away a lot of crud, and wiping the battery off with a clean, dry one will finish up the process nicely.  You should also take a quick look at the electrolyte level in the battery cells, bringing it to the “split ring” with distilled water.  Next, before “laying up” the battery, give it a full charge, then disconnect it, and let it lay. What’s a full charge?  Assuming you’re working with a standard flooded acid battery, a full charge is 12.63 volts, measured after the charger has shut off and the battery allowed a few hours to rest without the charger or any load on.  Use a digital test meter to make this determination. 

If your RV is equipped with solar panels, then leaving the battery in their care is a natural.  We leave our solar-equipped fifth wheel and our truck camper disconnected from shore power when not in use. The solar panels on the roofs of these rigs are connected to the house battery systems via a solar regulator that doesn’t allow for overcharging.  The batteries are up and ready to go whenever we are. 

We have a similar situation in a runabout car that we leave stationed with one of our rigs. It may be a period of several months between car uses, and we’re not big on leaving a smart charger hooked up under the hood of the car. Instead, we have a solar-powered car battery maintainer hooked up to the car.  In the years that we’ve used this system, we’ve never had any disappointment.  We simply arrive, disconnect the solar panel from the car through a “quick disconnect” system, hop in, and hit the key.  When it’s time to put the car back in “storage,” we cover it with a car cover and reconnect the solar maintainer. 

Keep your batteries propped up on a two-by-six?  Yeah, and make sure you don’t crack your knuckles either; after all it’s hard to pick up a car battery with arthritis in your fingers!

Russ and Tiña De Maris are authors of RV Boondocking Basics—A Guide to Living Without Hookups, which covers a full range of dry camping topics. Visit for more information.

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