Actual soldering was determined to be unsuitable way back with Ni-Cd rechargeable/disposables because solder just isn't quite a good enough conductor of electri

Actual soldering was determined to be unsuitable way back with Ni-Cd rechargeable/disposables because solder just isn't quite a good enough conductor of electricity for the duty. Plus when current is flowing, where more resistance is encountered will be the places where more heat needs to be dissipated, and solder melts too easily. Which is why they factory-welded them at instantaneous temperatures beyond the melting point of the interconnection itself.