Watthour
Electron Rancher - JS3600
Desolder each pad one at a time, then use a solder aid of some sort to push the power pack lead away from the pad. Move on to the next, etc. A pencil can make for a good solder tool if you don't have a dedicated one - Lead solder will not stick to the carbon of the pencil. When you're done the pack can be removed for some testing, and the excess solder on the circuit board can be removed with copper wick, a solder sucker, or whatever method is most convenient.