Flat eneloops

[Tim Streater]

My garage door proximity sensor is still going through AAs at a surprising rate, so I'm putting Eneloops in for the moment. I changed a pair today (after 3 months or so), as the main controller was bleating that it could no longer find the sensor. I then measured their voltages, and one was down to about 0.85V, but the other showed some

40mV. Put them both in the charger and they just finished, both now showing 1.45V.

Interesting to see that the sensor works with quite a voltage range, but why would one Eneloop be down to 40mV with the other a lot higher?

[Chris Green]

Because they're not identical capacity, just fairly close.

It's one of the problems with running rechargeable cells in series, it's inevitable that some will discharge completely before others and, as a result, the weaker cells get reverse charged if you continue to use the device. NiCd cells *really* don't like being reverse charged, I'm not sure about NiMh ones.

[Dave Plowman (News)]

Seems to happen with re-chargeables in series more regularly than with alkaline. Don't know the reason. Except perhaps they keep a more stable voltage before dying quickly. I notice it most with this mouse.

[Brian Gaff]

No they don't either. I think that my charger does not charge them in series but I do notice that there is always one that looks charged but always goes down before the other in a 2 series cell system. Originally the equipment actually use four but they were two in series which were both put in parallel with the other which made them last less long than just two on their own as the current presumably see sawed back and forth making them self discharge. Brian