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Single battery dead of 2 in series

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Recently, my digital camera (2xAA Ni-MH) batteries have been dying much quicker than normal when the camera is sitting unused. Annoying, but I didn't think much of it.

I've had my house for about 5 years and didn't realize my thermostat even had batteries (2xAA) until they died recently. I popped them out and reached for my fully-charged batteries from my camera, only to discover they were dead (again!). Getting curious, I decided to check the batteries from the camera and the batteries from the thermostat with my DMM. In both cases one battery was completely dead and the other battery read 1200-1400.

Why would this happen? In both cases the batteries are connected in series.

I suppose the previous owner may have put mis-matched batteries in the thermostat, but they are visually identical.

In the case of the camera, I've been using the same pair of Ni-MHs together and charge them together.


how long did you use the batteries?

they do not last 1000 cycles, maybe 100 or 200,
since the flash is quite a current surge.

I'd just replace them with new batteries.
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