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June 15, 2009 5:32 AM

Do batteries lose charge?

I am thinking about buying a larger lot of CR2032 and AA batteries off ebay. I am probably going to need many years to go through them. Batteries usually have expiration dates, do they really hold most of their charge until then or do they practically become useless before that? Also, does anybody have experiences with buying batteries off ebay?

posted by Brennus to technology (8 comments total)

Yes, batteries lose their charge while being stored. I'd recommend buying some nice rechargeables instead of a bunch of standard AA.
Data point: I bought a bunch of CR2032 off of eBay 4 years ago and they still work. I have no idea what charge they are at though.

Alkaline batteries stored at "room temperature" self discharge at a rate of less than two percent per year. So normally refrigerating or freezing them will only help maintain their charge by a tiny amount. Hardly worth the effort of chilling them. However, if alkaline batteries are stored at higher temperatures they will start to lose capacity much quicker. At 85 degrees F they only lose about 5% per year, but at 100 degrees they lose 25% per year. So if you live in a very hot climate or are storing your batteries in a very hot location, it may be worthwhile for you to store your alkaline batteries in a refrigerator instead.

NiMH and NiCd batteries self discharge at a MUCH faster rate than alkaline batteries. In fact, at "room temperature" (about 70 degrees F) NiMH and NiCD batteries will self discharge a few percent PER DAY. Storing them at lower temperatures will slow their self discharge rate dramatically. NiMH batteries stored at freezing will retain over 90% of their charge for full month. So it might make sense to store them in a freezer. If you do, it's best to bring them back to room temperature before using them. Even if you don't freeze your NiMH batteries after charging them, you should store them in a cool place to minimize their self discharge.
linky
posted by zephyr_words at 5:43 AM on June 15

I've got three left in a 5-pack of CR2032's I got on ebay. One went into my wife's laptop, the other into one of our Volkswagen key fobs, and I've got extras. The remaining batteries are marked with expiration dates in December of 2012, so I'll probably actually use most of them. I bought name-brand batteries from a domestic seller with solid feedback, and am happy with the purchase.
posted by jon1270 at 5:56 AM on June 15

Also depends on how old they already are. Maybe they are on sale because they are already 5 years old?
posted by gjc at 6:11 AM on June 15

More than you probably want to know about self-discharge (and batteries in general) can be found here. They also have information on the best way to store different batteries if you do decide to go ahead and buy in bulk.
posted by TedW at 6:48 AM on June 15

Just like our minds, the battery is either charging, or discharging. There is no such thing as perfect stillness. Idleness is its own form of loss.
posted by discountfortunecookie at 9:33 AM on June 15

Years ago I did a science project on batteries, so I have some jargon to inject into the discussion.

First, what the OP wants to know about is the Shelf Life of batteries. Like canned goods we can discuss batteries the same way.

But batteries have a certain quantity called Internal Resistance, which increases over time. The amount of time until the battery becomes unusable depends on the battery type, and the application. The internal resistance of batteries sitting on the shelf increases far more slowly than when the battery's being used, but it is increasing. And Brennus, to be completely accurate, a battery stores electrical voltage, not charge (for the latter, see: capacitor).

Standard (flashlight) batteries' internal resistance increases faster than that of Alkaline batteries -- hence alkaline batteries last langer (but they cost a little more).

However, if you really want to save money, and be a friend of the earth as well, spend even a little more upfront and buy rechargeable NiMh batteries and a charger. Incredibly, these batteries will last hundreds of charges (although to be truthful, between chargings, they don't last quite as long as a fresh Alkaline).

I have several little AA appliances, and I swear by rechargeables, and feel sad for the people I see stocking up on so many Alkaline batteries -- such a waste!
posted by Rash at 11:34 AM on June 15

And if you go the recharable route (as I have) I reccomend Eneloops. (Google for more endorsements.)
posted by Brian Puccio at 12:33 PM on June 15

Seconding Eneloops. They're a special kind of NiMh rechargable that, when sitting on the shelf, lose their charge much more slowly than ordinary NiMh.
posted by exphysicist345 at 9:11 PM on June 15