TS18S problem

Was given one of these recently, it seems to switch itself off with no
warning, even though the battery appears to have life in it. But switching
it on again, it turns itself off while searching for a network, which does
make it seem like a battery problem.

Searching on the net, I see there was a known defect with these, wherby they
would switch off randomly. Is the cure for this known?
I've cleaned the battery contacts of course.

Help and suggestions are very welcome.

Regards
Gary