Ralf:

Yes, I do have the battery replacement instructions.  I will bring them home from the airport and make you a copy.  Send me your address.

BTW, Matt Hapgood sent me the model number (M48TO2-200PC1) but Digi-key did not recognize it  so I'm still looking.

 I replaced the battery about 4 or 5 years ago but since I have the panel out, I decided to replace the battery just because its a pain to get to.

Regards, Bill H