Can I keep batteries in their charger indefinitely?
April 27, 2004 8:20 PM   Subscribe

I have a Sony Clié that takes alkaline batteries. Sick of the cost of fresh AAAs, I recently bought a charger and 4 Ni-MH batteries (1.2V 700 mAh), intending to keep 2 in the Clié and 2 in the charger.
Question: if I keep the unused batteries in the plugged-in charger permanently, will they explode or otherwise be ruined? If I keep them in the charger but keep it unplugged, will they lose their charge? The charger has a "charging" light which doesn't go off as long as it's plugged in, and has a "fast charge" light which goes off after 5 hours.
posted by signal to Technology (10 answers total)
 
My NiMH charger turns off once the batteries are charged. I assumed all NiMH chargers work this way, because overcharging will damage them. Maybe the "manual/sheet of paper" that came with your charger has the answer?

Also, my (old) Handspring Visor can't use rechargeables, according to the manual, because it can't accurately predict remaining power. I don't know if this is an issue for the Sony, but worth looking in to.
posted by teg at 8:56 PM on April 27, 2004


Why not simply charge the extra batteries as needed? If the fast charge takes five hours, slip them into the charger the night before you need them, and put them into your Clie when the old batteries die.

NiMH, if I'm not mistaken, do not have a memory built in, unlike Lithiums. Therefore, you should only charge them fully when they're completely dead. (I could be wrong about that; I haven't used Nickel-based batteries for years now)

And yes, they will lose their charge, but almost negligibly slowly, depending upon the quality of the battery.
posted by BlueTrain at 9:12 PM on April 27, 2004


teg, there's a hack for the Visor to make it read rechargebles fine. You should be able to find it at visorcentral.com if that site's still around. It's something like period symbol 7 from within the notepad app.
posted by dobbs at 9:44 PM on April 27, 2004


You should not leave NiMHs on a fast charger any longer than is necessary to charge them. However, on a slow charger, it's generally fine -- the current isn't enough to damage the batteries noticeably.

And no, you should not discharge them all the way before charging them again; that's a good way to wear them out before their time.
posted by kindall at 11:05 PM on April 27, 2004


NiMH batteries lose 1% of their charge per day just sitting around. So some chargers have built in trickle mode that delivers the right amount of juice so that you can store them there without damaging them. If your charger has that (it's fairly common), then leave them in and you're good to go. If not, don't do it.
posted by _sirmissalot_ at 11:12 PM on April 27, 2004


And no, you should not discharge them all the way before charging them again; that's a good way to wear them out before their time.

That may be solid advice, but I have been informed to do the complete discharge cycle two times when the batteries are brand new. This was from a Nokia manual and then from a battery manufacturer pamphlet. It at least hasn't damaged the batteries and they seem to last a very long time, so I'm happy.
posted by _sirmissalot_ at 11:17 PM on April 27, 2004


I have been informed to do the complete discharge cycle two times when the batteries are brand new.

That's probably for a lithium ion battery, not a nickel metal. My Apple Powerbook manual said the same thing.

In a related matter, Verizon Wireless has been advising customers not to overcharge their cell phone batteries.
posted by werty at 8:10 AM on April 28, 2004


A couple of links. Hope they're useful.
posted by BlueTrain at 8:44 AM on April 28, 2004


Response by poster: Well, the green light on the charger is labelled "fast/trickle", so maybe it has some sort of trickle mode after the battery is full. Batteries haven't got hot yet, which Blue Train's links say they will. No real instructions in the box, alas.
Thanks, all.
posted by signal at 8:59 AM on April 28, 2004


That's probably for a lithium ion battery, not a nickel metal.

woops, you're right about that.
posted by _sirmissalot_ at 12:48 PM on April 28, 2004


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