looks like it's probably sub-c cells (slightly shorter and skinnier than a c-cell). If you brought the battery pack to my store, I would charge you $21 for a rebuild w/ 1 year warranty. At this point, your best option would be to find a battery store or a company that does power tool battery rebuilds. The 3 cells need to be tack-welded together along with the tabs or wires that attach it to the tool. It looks like they probably have standard flat spade terminals tack-welded to the battery and wire leads that clip onto them. Otherwise, you may be able to pick up some tabbed sub-c's for around $3 each and go to town with a solder gun.
Can I reply with less words? No...
My moral compass is broken - I used to play with magnets as a kid.