Hi,
Why recharge it. Just stuff in AA batteries, Alkaline, Energizer, Duracell, etc. and calculate for a long time.
Throw the cells out when they die out. Thats what I've been doing since I acquired a 34C .
Seriously because its an AA fit, you can get AA cells
of your choice (NiCad if you like) and just stick them
into there.
Remember that the + terminal is the one closest to
the center of the calculator. Suggest marking it
into there with a black fine-point permanent marker.
To bridge the far end, you use some sort of very thin
metal foil. Aluminum in a pinch, though its kind of
soft and crumbly. I have a piece of thin copper-braid in there presently, you know, its called "Solder Wick".
Some .003" nickel foil would be perfect.
If you put in NiCad AA cells, you can charge the same
way that HP had in mind originally.
Good luck !