Refreshment of rechargeable batteries?

[Physikfan]

Two rechargeable batteries, one NiCd battery D and one NiMH battery C
can not be recharged after 2 years of very moderate use:



Both batteries were used in two different groups of each four identical batteries of the same type.
The three others of each group still work perfectly.

Now my question:

Please who knows successful refreshment procedures of such batteries from personal experience?

[BradC]

Please who knows successful refreshment procedures of such batteries from personal experience?

It depends on their failure mode. In all honesty the best "refreshment" is to replace them.
You *may* have dendritic growth that can be "remediated" in the short term with a good "zap", but the resulting hole in the insulator will ensure they re-grow so it's really only a short term "fix".

Provided you've been looking after them (ie not letting the pack discharge to cell reversal, not overcharging or overstressing the batteries) then you have some failed cells. Any "rejuvenation" you apply will be at best short term and vaguely useful.

[all_repair]

Not worth the time and electricity even you are successful.  You need to slow charge and discharge, maybe 3 cycles, and with no guranteed result.