Here is how you do it. Needless-to-say, it you don't have the skills, don't do it. The risk is yours!

1)Take an Xacto knife and run it along the long sides of the battery container to cut the 6 dots of glue that hold the cover on. You can also use a small screwdriver. The plastic is pretty flexible.
2)You will see 4 pink NiMCa rectangular batteries wired in series with a fuse on the bottom. Lift the battery pack up and cut the tabs attached to the bottom cover close to the batteries. Mark the tabs + and - so you wire in the new set correctly. You can desolder the fuse link if you wish and reuse it.
3)The batteries you removed are Toshiba F3's which no one seems to have for sale. Their EXACT replacement is Sanyo TH900F5 (1.2V)You will need 4 of them per TT2 battery pack you wish to replace.You can get them at Battery Tech([email protected]) 800-442-4275. They will even solder up the packs with the fuse link if you wish.Those of you on Long Island NY can pick them up. They are located in Hicksville.
4)Solder the new batteries to the tabs you cut earlier and pay attention to the polarity. Keep your soldering pencil away from the batteries.
5)You can glue the cover back on or use electrical tape to hold the cover on if you wish. Now charge the pack up and you are good to go!