How can I tell if rechargeable batteries are dead?

I have a few AA and AAA rechargeable batteries kicking around – they’re probalby 5 or 6 years old. I charged up 2 sets of 3 batteries to use in the walkie-talkies on Saturday’s ride, yet within half an hour of setting I was getting the “low battery” warning beeps. Seems to be that one of more of the batteries is dead, is there an easy way to identify it using a multimeter of the like?

For reference the AA are 2600mAh and 2700mAh vapextech, the AAA are 1000mAh. the charger is also Vapextech and is for NiMH and NiCad – not sure off hand which the batteries are, it doesn’t say on them

just found it – they’re NiMH

if they’re 5-6 year old id buy some more rechargable batteries (sometimes you can buy a set that includes the charging unit too ! (Bury market)Lancashire… good for stuff like that..tho it well may be along long way from you ( 😉

bump for the daytime crowd. new batteries is an option but if I can identify the ones worth saving it’ll be good

Any rechargeable that fails to hold a charge is usually spent.

Try cycling them a couple of times (running flat then fully charging)

5-6 years is a long time for NiMH (even those that are well maintained). NiCd can last much longer if looked after and charged with an intelligent charger (I have some that are 17 yrs old which are still serviceable).

When you buy replacements, get an indelible marker such as those used on blank CD’s and date the new ones. That way you will know what’s what going forward.

I recently bought myself a Technoline BL700 Intelligent Battery Charger.
Took a set of well-shonky batteries and refreshed them so they are now as good as new (took 5 days of charging/discharging but we got there in the end)

Not cheap but a worthwhile investment if you use batteries a lot.

http://www.amazon.co.uk/Technoline-BL700-Intelligent-AA-Battery/dp/B003S4JQS2

What’s the best way to run batteries down?

When my lights are running dimmer I leave them on ready for recharge but it still takes ages for the charge to be spent.

If one cell (in a pair/three/four) is dying, it’ll run flat first, and then the other cells will reverse charge it, and damage it more. So, you need to find the duff cell. For that you need a battery tester.

Because not all cells are equal, running them down needs to be done on a single cell basis (or you’ll end up reverse charging the worst one again).

At 5 years (ish) old, and about £1/cell, maybe just buy some new ones?

If one cell (in a pair/three/four) is dying, it’ll run flat first, and then the other cells will reverse charge it, and damage it more. So, you need to find the duff cell. For that you need a battery tester.

Ok, so I need a tester, can it be done with a multimeter? I’m not an electrical engineer.

All hail the BL700!

Ok, so I need a tester, can it be done with a multimeter?

Yes – just check the cell voltage. NiMH are fully discharged at ~1V, so if any of your cells are going down to this quickly (after a few cycles) then they’re dead.

For cycling batteries you don’t need to fully discharge. Try not to reverse charge your cells whilst you’re cycling them – though the chances are any cell which runs down much faster than the others won’t be much good after cycling, so not worth worrying about that much.