while he was there, he checked the battery and it was like new! the charge was still more than 3 volts (like 3,18!) after 29 years! cool! so at least I'm not gonna replace the battery anytime soon...
anyway when it will be the time, I guess I'd want a battery holder instead of the soldered battery...
hope to have good news soon... I'll let you know how it will end up! thanks anyone who contributed this topic!
Fabio