Wow that is certainly something! You say its potted in resin, so assuming some sort of epoxy or possibly polyester resin. Either would be very tough to deal with. There are some relatively nasty solvents that 'might' weaken the polyester a bit... methylene chloride and tetrahydrofuran come to mind. The epoxy would be even tougher. You could easily spend a pile of money on solvents and hours/days of your time only to find you still have a virtually unusable lump of battery.
If I had to do it, I think I might work to pretty that up a bit and see if you can sell it, then buy/build something more along the lines of what you need.
Good luck!