Christopher Tidy wrote:
CS wrote:

I have some lengths of cooper bar - 1 inc x 1/2 inch x 5 inch - used
as interconnectors on 2v battery cells. (...)

Unless you need to use lead free solder, I would use traditional
lead-tin solder. The general consensus seems to be that lead free solder
is less satisfactory and more difficult to work with.

What Chris said. Leaded is better.
Plus, if you are generous with CLEANING and FLUX and heat before applying solder, you will
be rewarded with a nice, shiny finish.

Remember to wash your hands after working with any leaded metal. Please keep your face
out of the smoke.

--Winston