For a lot of businesses, lithium batteries are a common part of day to day operations. Consider the batteries for the maintenance staff’s power tools, the handheld scanners on the shop floor, the floor scrubber, the two way radios, the e-bikes in the delivery fleet, even the batteries from equipment that is no longer in use and sold or scrapped. Most batteries spend the majority of their time waiting. There is a bigger chance that a battery at a storage or charging unit will be waiting, than being charged. Despite this, there are no formal routines to manage lithium battery storage. There are routines for charging, but battery storage routines are non-existent.
The way that waiting batteries are stored impacts how much batteries will hold a charge, and the risk of a waiting battery starting a fire. Most of getting battery storage the way it should be done is totally free!
The charge level is the most important factor when it comes to battery storage.
The ideal place to store a lithium battery is at a partial charge. The ideal level you should store a lithium battery at is 40-60%.
Full surprises. A battery stored at 100% is under more internal stress and ages faster. That battery would age faster sitting on a shelf than one stored at 50% — so the store’s habit of topping everything before it goes on the rack is the worst routine for batteries that wouldn’t be issued for awhile. Empty is worse for a different reason, the lithium battery self-discharge slowly, and one stored flat can drift below the voltage its protection circuit will allow it to recover. A battery that is left dead for six months may simply refuse to charge and a deeply discharged battery that is forced back to life is one of the less advertised fire risks in the whole subject.
That means a long term storage routine would include a partial top-up for anything that had drifted low and would require a periodic check, the frequency of which would be, on average, every few months. Where there are a significant number of spares, it deserves to be someone’s named job rather than everyone’s assumption, the same way fire extinguisher checks are. Lithium battery storage is not quite fire-and-forget, but it’s close, and a fifteen-minute quarterly walk around the racks covers it.
Cool, Dry, and Outside of the Equipment
Temperature is the second lever. Nothing good happens to lithium cells when the storage warms, so the storage must be cool. A frost-free store at 10 to 20 degrees is ideal (the mezzanine above the compressor and the van in July are not). The cold is less damaging than the heat, but a battery shouldn’t be charged when it is cold, so stock kept somewhere chilly needs time to warm before it is charged.
Dry is important because the battery terminals corrode, and corrosion with lithium batteries is a big problem (ask the devices that ferry us through life). Also, spares store best out of the equipment, not in it: most kit draws a trickle even when switched off, which slowly flattens the battery, and a battery sitting in a machine at the back of the workshop is a battery that is not getting checked.
There are two storage habits worth breaking. Batteries shouldn’t be stored loose in bins or drawers with metal (or anything for that matter). That leads to terminals shorting. That could cause a fire. Batteries belong on racking, with terminal covers on, standing on their bases, or in the original packaging. And they shouldn’t be heaped; a bit of air around each battery costs nothing and is doing quiet work.
Where the waiting happens
A lithium battery, about as benign as it gets, half charged and in good health, cool and dry, is relatively harmless given that there are few storage failures. Few, however, doesn’t mean never, and the same concern for the storage of lithium batteries in any amount, applies when charging them: if a battery ever vented, what is it stored next to? A battery problem, and a location problem, is a stack of lithium-ion batteries next to a solvent cabinet, under the sprinkler exclusion zone, or in the only escape corridor. This kind of problem will be identified by a fire risk assessor because storage of batteries will be viewed in the context of the charging of batteries.
The more of something you have, the more you need to consider the location. For example, a dozen batteries in a maintenance department, stored in a steel cabinet away from combustibles is probably adequate. A warehouse full of batteries, ebikes, a delivery operation full of batteries, or anything stored in an unattended building overnight is where fire rated lithium battery storage should be considered. These cabinets should provide a similar 90 minute fire containment on the storage side as they do on the charging side.
Quality batteries, when stored properly, will last a couple of years and still be just fine, aside from a little bit of self-discharge. Meanwhile, batteries stored fully and warm, in the equipment, left alone for two years become old stock, partially unrecoverable, and will most likely be the incident that brings relevance to the rest of these articles. For a site’s entire battery population, the difference between the two instances is just a quarterly walk around the racks and a one-page storage routine.