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I have a 90's handheld CB that I'm powering using 10x1.2V NiMH cells all in series. Because these cells are rather old (at least 8 years), when I got a low voltage warning, I decided to measure all the cells one by one. Originally they were charged together, now some of them are still at around 1.2-1.25V, some are down to 0.9-1.0V, but a couple are measured by my voltmeter to be about 0.02-0.07V.

My first guess is that they are old and damaged and belong to the dumpster (the appropriate one of course), but I'm not sure. So I would like to know what happens in the cell to reach this stage and if they sustained permanent damage or they can be safely recharged.

Mauro F.
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    I would try to CC/CV charge all cells to 1.2 V before throwing it away. – winny Jan 07 '21 at 10:03
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    The ones that have more than say 0.5 V will very likely recover when you charge them slowly ( I would use C/10 so, on a 500 mAh cell, I'd use 50 mA). The ones below 0.5 V: just try the same. If they do not recover (the voltage stays low) as a last resort, I would "push" 1 A or more through them **for a few seconds only** to see if that does anything. Unlike Li-Ion based cells, NiMh cells can often (not always) be discharged to 0 V without causing much cell damage. – Bimpelrekkie Jan 07 '21 at 10:10
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    In my experience, the lifetime of NiMh cells can vary hugely. I have some Philips AAA I bought 20 years ago and they still work quite well. Many other cells had a much shorter usable lifetime. So don't discard the battery before at least trying it. – Bimpelrekkie Jan 07 '21 at 10:13
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    As long as the cell voltage hasn't actually gone negative, then there's a good chance they will survive a gentle rescue charge. However, in a series pack with some cells good, the bad ones will often have been reversed by the good ones. So charge carefully, and see. – Neil_UK Jan 07 '21 at 10:46

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