Fred wrote:

I am trying to replace a couple of sub-c nicads. Something that should
be so simple is not going smoothly!

Is there a trick to soldering the tags of two cells together? It has
taken me ages and the result looks untidy. What trick am I missing?

You tin each tag on its own first (i.e. melt solder onto them).
Then you position the two cells so that the tags overlap, apply a
blast of heat, and let the two blobs flow together.

Chances are that this positioning is the critical part of the
operation and requires more hands than you have, or is awkward
because of the way the cells need to fit together when done.

If so, it may be better not to solder the tags together, but to
take a short length of wire and solder one end of it to each tag.