I really don't like proprietary hardware, and these batteries are no exception.
I went looking online for replacements but what I have found is that they are no longer manufactured and go anywhere from $60 to $120... What a scam!
Even if you buy new old stock, it is likely that the batteries will not be reliable because they have just been sitting around likely dead.

With the knowledge above I decided to rip one apart because I noticed that they are 4.8 volts and are Ni-MH. That got me wondering if I could use AAs to replace the cells, turns out you can! The board in the actual pack has contacts that are not soldered to the cells! This aught to be easy enough.