"Andrew Rossmann"

Has anyone had any luck in replacing individual cells?

** Best to replace the lot.

There are no
markings on the batteries, so I have no idea what their capacity is.

** See above.


These are chained together with short metal strips that are spot-welded
to the batteries. How easy/hard would it be to solder to them, and will
it damage the batteries if I try?

** Try to get cells that have tags fitted to them.

These are very easy to solder with any decent soldering iron and flux cored
solder ( not lead free) as used for electronic work.



..... Phil