Storing Rechargeable Batteries
Cy Cheze wrote:
NiMH batteries must be recharged frequently. Otherwise they lose their ability to be charged or recharge at all, after only two or three months. At that point, they are almost impossible to revive, or function only briefly as "zombies." Buy NiMH only in quantities consistent with current needs, and use and recharge them regularly.
That can be somewhat true, though I've had nimh batteries take a charge after a couple years of sitting around.
There are also NiMH batteries that are specifically designed for a lot less self-drain - the Sanyo Eneloop's and the Rayovac "hybrid" batteries come to mind.
As for Li-ion batteries, I've yet to confirm a "real world" life span or charge-cycle tolerance. Some I've now had for three years have definitely lost capacity. I've done no precise tests, but simply mistrust them and use them as reserves.
Lit-ion seem to degrade simply because they're sitting around, whereas lith-ion degrade as they're used (in gneral).
Cell phone users have to be the experts on Li-ion longevity.
The greatest fear lurking in the mind of any prospective buyer of a hybrid or all-electric car has to be whether, upon resale, the cars won't fall in value by year 5, as potential purchasers worry about the battery longevity.
While not entirely untrue, the Toyota Prius (the stereotypical hybrid car) has one of the best resale values of any vehicle can buy. It also takes special steps to keep the battery lasting a long time - it never completely charges or discharges the battery (apparently nimh lasts much longer if it's never charged or discharged more than 30% to 70% - or something like that), it uses the air conditioning to cool the battery while the car is running if it's needed, etc etc. There's a bunch of other stuff that's really, really expensive to replace on a car - on a Buick I owned fixing a broken power window and a blower fan that was wearing out cost me $500 because the labor costs are so huge. Replacing an automatic transmission that's worn out can costs thousands of dollars. Etc etc - there's a whole bunch of crap on a car that can wear out and be really expensive to replace.
Anyways, what I've read with lith-ion is that ideally you want to leave the battery at 50% charge and store is somewhere cool. Supposedly heat really shortens the lifespan of lith-ion batteries (which is why laptop batteries have a short lifespan - all the heat the computer generates).
Actually, wikipedia probably says it best -
Prolonging battery pack life
Depletion below the low-voltage threshold (2.4 to 2.8 V/cell, depending on chemistry) results in a dead battery which does not even appear to charge because the protection circuit (a type of electronic fuse) disables it. This can be reversed in many modern batteries, especially single-cell ones, by applying a charging voltage for long enough to make the cell voltage rise above the low-voltage threshold; however this behaviour varies by manufacturer.
Lithium-ion batteries should be kept cool; they may be stored in a refrigerator.
The rate of degradation of Lithium-ion batteries is strongly temperature-dependent; they degrade much faster if stored or used at higher temperatures.
Lith-ion batteries also don't lose their charge very fast just sitting around.
You can take steps to maximize the battery life of a battery just sitting around, but sometimes it's not worth the hassle to take extra measures. The big thing is just to not store a completely depleted battery, and to not store the batteries anywhere where it's really hot - like don't store them in a hot attic, near the furnace, sitting in the sun, etc.