On 20:11 3 Apr 2020, Nick Odell said:

On Thu, 02 Apr 2020 12:52:25 +0100, Pamela
wrote:

On 20:34 1 Apr 2020, Nick Odell said:

One AA cell has suddenly turned grey underneath the transparent
printed sleeve and it looks like a powdery coating has formed there.

Under normal circumstances I would just throw it away but these are
not normal circumstances (I´m about 8000 miles away from my stash of
spare batteries and over here I´m not allowed out to buy any more) so
I´d like to keep using it for as long as it holds a charge if it is
safe to do so and it will not ruin my equipment.

Any thoughts about whether this might be just corrosion on the outside
of the can or might it be leaking chemicals or is something else
happening?

Thanks!

Nick

This can happen if the cell is overcharged.... snip

That mention of overcharging concerns me. I thought all chargers these
days automatically cut out when the battery was fully charged or after
a certain period of time had elapsed? I am currently (sorry about
that) using a two-cell usb-powered charger from Screwfix which blinks
while it is charging and shows a steady light when it has stopped.
(Most of) my other cells run to the end of their charging cycle and
then stop. These ones, I admit, just go blinking on and on.

Nick

Although there are several ways of deciding when to terminate charging, a
cheap charger may only use one and even then not sense the moment
correctly.

For example, a common way is to sense a voltage dip as full charge
approaches but NiMh cells, unlike NiCads before them, change voltage by
only a small amount and a poor charger may fail to sense it.

Excess discharge can also make a cell vent but maybe not in your case.