Thanks a lot for the replies so far!

I hope the battery's not dead! When I tried to take it out last year
(when I first started this job) it would NOT come out of the mower body,
following the manual's instructions. I may have to take the mower apart
to get the battery out.

I will have another go at charging next time I'm across. And No Dave,
I didn't charge it last thing last autumn, mainly because (having
successfully charged it when I took this job on last year) it always
started first time thereafter (it takes about 90 minutes to cut the
grass).

Cheers for now
John