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!

Is the listed amp hour rating the same, greater or lesser than the toshiba model?

There are no ratings printed on either battery battery and I do not have access to spec books. I suspect that all these batteries are used commercially or shrink wrapped in packs for various devices. It is working for me as expected. I have another battery source looking into replacements as well. I have not heard from him yet. Will post his URL If he comes up with something viable.
It would be nice if RTI would provide user-replaceable batteries for their future products so it doesn't cost on the order of $100 to replace a pair of batteries. Other companies are doing this. It is one thing to charge alot for a good product, but quite another to have a high on-going maintenance cost which can be avoided. When battery packs are propriatery and that company can go out of business, it is the hapless consumer who also bites the bullet. Many of us thought that RTI was, in fact, going down for the count.