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