I have not built this circuit yet, but Nichrome gets hot with electricity. If I have button batteries in holders, connected in parallel, and Nichrome wire on the end, won’t the connectors on the button battery holders just end up melting?
Sounds like a legitimate concern. So connect the nichrome wire to copper wires with lower resistance and sufficient length (so they don't heat up too much on the battery end) which you in turn connect to the batteries.
Btw, using button batteries for generating heat sounds like a good way to consume vast numbers of button batteries in a short period of time.
Google showed this as a first reply: Do not try to silver solder the nichrome wire directly into the circuit--just tin it with the silver solder and then regular solder works FB to attach it to tie points or ...
I wonder if this is a follow up on the earlier thread a week or so ago about achieving really high heat with button cells. I didn't look it up, but similar questions were raised. It almost sounded like some kind of pyrotechnic igniter to me for one time use. To be Frank, the possibilities worry me a bit.