Proper Way to Charge NiMH Batteries

Benjamin, the answer is "yes."

Yes, NiMH is newer than NiCd, and it has very little of the memory effect that was the big complaint about NiCd. Also NiCd had some toxicity problems when disposed of.

With most modern battery chargers, the charger will sense the current flowing into the battery, and when it nears "full charge" state, the charger will taper off the current. However, it seldom shuts off the current completely. Some will continue to give little pulses of charge current just to keep the "full" battery topped off. In the short term, that doesn't do a lot for you. In the long term, it will offset the small self-discharge of the battery. However, that little pulsing charge will keep the battery warmed up. That has some positive effect in keeping the battery ready to go, but it has some negative effect by "baking out" some of the chemicals of the battery. So, it is probably not great to leave the battery in a constant pulse charge state forever. It is probably better to run the battery down more than halfway and then charge it back up to full. There will be some variation on these guidelines as you change from one battery brand to another. Some chargers are pretty stupid, and some are very intelligent.

–B.G.–

Computer batteries are lithium?

"Computer batteries are lithium?"

Some are lithium ion, and almost none are lithium primary.

Some are nickel metal hydride. There are a few old ones that are nickel cadmium. There are a few other chemistries.

–B.G.–

Regrettably, smart chargers are darn rare. Anything you pull off the rack at Target is going to be a dumb charger (i.e., the ones sold with sets of NiMH cells).

Over the long haul, if you accumulate a lot of rechargables it's a good idea to invest in something like this, which can run break-in cycles, refresh cycles and recovery cycles. They're also excellent for matching up battery sets of like capacity.

http://www.amazon.com/Maha-Powerex-MH-C9000-WizardOne-Charger-Analyzer/dp/B000NLUSLM

Cheers,

Rick

"Some are lithium ion, and almost none are lithium primary."

What would Apple's 10 hour 'lithium polymer' batteries be?
http://www.apple.com/macbookpro/battery/

Apple's lithium polymer battery is rechargeable. Therefore, it is not a lithium primary battery. It is a lithium battery, somewhat similar to most of the rechargeable batteries that go into small cameras these days. This type of lithium cell has a voltage that varies around 3.7 volts when charged.

You can always spot a lithium primary battery, because it will have a completely different voltage, typically around 1.6 volts when new.

Yes, I thought you would get a charge out of that.
[edited to correct]

–B.G.–

If you go to Amazon and look up the Maha or LaCrosse chargers, look for reviews by NLee and then read the comments to his reviews. That is an active ongoing discussion of these sorts of issues. NLee is an engineer who knows a lot about these things. He is also great about answering questions in the comments thread.

–MV

I've been using a LaCrosse charger for the last couple of years, and it's been quite good. AFAIK it shuts down when the batteries are at full charge rather than pulsing them, but I could be wrong. I haven't left batteries in it long enough to find out.

It has a reconditioning mode that's been pretty successful in making batteries that seemed to be dead start working again.

Terminology gets messy when we discuss batteries. The LaCrosse charger and ones like it are intended to recharge individual cells, such as type-AA. You might have four AA cells lined up in the charger at one time. Some chargers are smart enough to figure out which one of the four is the weak one so that you can exclude it and replace it.

A completely different kind of battery charging takes place in a laptop computer battery. There, you do not have individual AA cells or anything else that you can separate. Either the entire battery pack is engaged, or it is not. Those battery packs are typically twice the size of a pack of playing cards.

Benjamin's inquiry was about the latter type of battery pack in a NiMH chemistry.

–B.G.–

I understand lithium polymer batteries are the next generation in this race.

Any knowledgeble folks know about them?

BTW, I read that some new electric cars may use Li-poly batteries soon.

"I understand lithium polymer batteries are the next generation in this race."

That is certainly what Apple Computer would have us believe.

Almost any time I see a laptop computer manufacturer making claims about 1000 charge cycles, I believe half of it for real life use.

–B.G.–

The Googles tell me Li-ion polymer cells were introduced in 1996, so it seems likely that some proportion of batteries labeled simply "Li-ion" are of the polymer persuasion. They're evidently more flexible than standard cells, so can be made into weird shapes and (tie-in) they're lighter.

No major performance gains though, from what I read.

Cheers,

Rick

p.s. My HP laptop utilities occasionally bug me to completely discharge and recharge the battery to recover its capacity, so evidently Li-ion cells do experience some amount of charge memory.

My understanding is that the Li ion batteries don't have significant memory, but that the chip which monitors the charge level gets confused after a while and needs to be reset by a deep discharge-charge cycle.

I think Bob's suggestion of letting NiMH batteries discharge a bit before recharging is a good one. I do however usually top off before I go out on a big hike.

Li-Ion batteries should be charged continuously from what I've read, although as has been pointed out a discharge-recharge is the only way to keep the metering accurate. Every time a Li-Ion battery is discharged, it loses some life.

With Ni-Cad batteries, a full discharge before recharging is the best way due to "memory effect."

HJ

"p.s. My HP laptop utilities occasionally bug me to completely discharge and recharge the battery to recover its capacity, so evidently Li-ion cells do experience some amount of charge memory."

Some laptop computer manufacturers are pretty tricky. In some cases, the software utilities will bug you to discharge and recharge the battery. However, that may not be for optimizing the actual battery. It might be so that the software can get a fresh measurement on what the current capacity of the battery is so that it can update the little "battery fuel gauge" more accurately.

–B.G.–

How well does re-conditioning work with newer batteries? With the exception of the batteries that came with my LaCrosse charger, most of my rechargeable batteries are… well, no longer spring chickens.

I had some luck with re-conditioning batteries back in the old days of NiCd, but I have not fooled around with it much since NiCd mostly went away.

–B.G.–

Great comments — thanks, everyone!

I think most of my older batteries are NiCd's, and I'm certain that my newer LaCrosse batteries are NiMH. I probably reconditioned NiCd's.