NiMh batteries

[The Medway Handyman]

Do NiMh batteries self discharge if left unused for a period of time, or is this just a myth?

[Dave Plowman (News)]

They do - as do Ni-Cads. But by how much seems to vary wildly by make. Or whatever. In other words you could have some which appear to take a full charge and last ok when used near immediately - but discharge very quickly when not used, as it were.

[ericp]

Two articles here. The freezer bit is interesting.

[chris French]

In message , The Medway Handyman writes

Yes, fairly quickly as well - can be noticeable in a matter of weeks?. Though the newer type with a lower self discharge rate really do hold charge a lot better. (Sanyo eneloop, Uniross Hybrio etc.) which is why they can sell them ready charged.

No.

Except for thing like the digital cameras, where we tend to cycle batteries pretty frequently anyway. I'm finding that I'm moving over to the lower self discharge rate ones when I get new ones. for general use I find them more convenient and they last a decent amount of time in low current drain applications.

[Grimly Curmudgeon]

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember "The Medway Handyman" saying something like:

Up to three months if left unused to the point where they're no use when you go to switch on a camera, etc.

[The Natural Philosopher]

yes. Bloody quickly too. It gets worse with age..

[robgraham]

Doesn't everything !

[airsmoothed]

I think 1% charge loss per day is normal for an NiMh; personally I've switched to eneloops which do seem to retain charge as advertised.

[dent]

The only trouble with the Eneloops, Vapex Instant's, etc. is that the capacity is much lower (e.g., 2000mah v. 2900mah), giving a much shorter run-time. I'm not aware of any power tools using the Eneloop- style batteries yet, but I imagine that power tool manufacturers would rather have the higher capacity and longer run-times, than longer on- the-shelf time?

dan.

[Dave Plowman (News)]

Really, if self discharge is a problem on a little used cordless tool wouldn't a mains one make more sense?

[ransley]

I dont find actual runtime less since they are not in my charger as much. With every charge you get less life, with eneloop after 2 years I am happy, my regular Nimh after 2 years have noticably less life compared to eneloop. Sanyos ratings on capacity I trust other off brands stating 2900 mah often are overstated. Try Eneloop, I read a new eneloop is or will soon be out with that will last even longer, my regular Nimh deteriorated very fast and are junk. When I used to turn on a camera with regular nimh It was always near dead, now with eneloops its not an issue anymore, my camera just works after sitting

3-6 months. I used to waste alot of time charging.

[dent]

That's very true. I use them mainly for my LED bike lights, where one set of 2900mah last me two days. Add in other uses (head torch, etc.) and over the course of a winter each set of batteries get an awful lot of fairly deep discharge/recharge cycles. Most brands I've tried die very quickly but I still have Vapextech batteries which are three years old, and still hold enough charge for the magic two days of use though. The Eneloop or Instant ones at 2000mah don't quite enough capacity to last 2 days though, so I would have to charge them every day.

I look forward to that. Over the summer months when my lights get less use I still have to charge them every 2-3 weeks even if they aren't used, and avoiding that would be good.

dan.

[ransley]

I think the new eneloops last longer by allowing more recharges, 1000 vs 600, I use regular alkaline batteries in my Led bike and regular lights and go all summer, I think 300 hours is what mine are rated at , but they are not real bright so maybe that is why.

[Harry Bloomfield]

The Medway Handyman wrote on 24/11/2009 :

Over days, weeks or months - yes. How well they retain the charge seems to depend in part on luck, rather than how much you paid for them. Keeping them in a plastic bag in the fridge, is supposed to help.

[BD]

Newer ones will retain significant charge for up to a year. The ones that come pre-charged are normally that type. Hybrio was one make, now superceded by uniross ultra.

They are more expensive, but I find them useful for a backup set.

[PeterC]

7-Day Shop is doing its own brand of these at a couple of quid less.

I saw somewhere a test that showed the 2100mAh hybrid cells outlasting NiMH of nominally higher energy when used in a camera - can't remember the details.

[AnthonyL]

One factor AIUI is that some higher energy batteries eg Energizer, have a high internal resistance, so it doesn't take long in some instances for them to be unable to power the device they've been installed in. I nearly threw away a digital camera because it would only last a few seconds with new batteries. I bought even higher capacity Energizers and it still would only last a few seconds. I bought Sanyo Eneloops and it now goes for months.