[lern_too_spel]

Is it even safe to weld an alkaline battery? I don't know.

Why not just solder the contact? If it's soldered, you should be able to swap the battery with a soldering iron. Sure, heating the iron and cleaning it will take much more time than swapping a battery in a spring-loaded housing, but I've spent just as long opening battery compartments held shut with tiny stripped screws.

[sokoloff]

Yes. The welding heat is VERY localized to the spots where the electrodes made contact. Very small spots and very localized heating for a secure connection. In this regard, less heat gets "into" the battery than would be the case from soldering, the operation is very fast (cycle times in the low number of seconds and welding times in the few milliseconds range), and more than strong enough for the application.

The better ones use a double pulse for a cleaner weld without the need for any flux.