Second, make sure to flatten your solder sites. I wasn't able to flatten mine so much that I ended up having a hard time returning the batteries to their original place, which made it impossible to assemble back everything into the casing. .

I didn't want to redo my solder as the plating I had left was quite thin and so I'll just wait till I need to replace the batteries again with new plating ready to replace as well. That is if the pump piston doesn't give up on me before then.