This is a DIY battery tab spot welder I made. There is a link in the intro that describes making and using one.

I spot welded a nickle strip to the minus end of the new battery. The new minus tab is aligned over the lengthwise Kapton strip.

An alternate method is solder to the battery. There are videos on youtube of people doing this. Presumably their projects have not caught fire (yet).

The online battery store that sold me my batteries says, "DO NOT solder" in the long list of disclaimers. This surprised me but it doesn't mean spot welding is safe. My first try spot welding on an actual cell I burned a tiny hole in the case and some fluid sprayed out. I thoroughly discharged the damaged cell and sent it to the HAZMAT bin.