I had similar problems with my battery pack, it got to the point when I would try to charge it, it would be hit and miss. I would have to jiggle the battery to get it to work, and that only work for a while, it finally quit charging.
So I pulled the cover off, and there's a wire that lays across the batteries. I think it's for a type of heat sensor to monitor the batteries from overheating when charging. Well it was broke, so I soldered it back together
and it works fine now with no problems. You may have to tug on the wire to see if it is broke, because I couldn't see where it come apart. There was some shrinkwrap on the end of the wires that you need to cut off or pull back. You will see a little black bead which is a sensor, be careful not to break that. By exposing those wires under the shrinkwrap you can check the connections make sure they are soldered good, if they are not you must re-solder them. If this is the problem the re-solder will solve it.