Ah yes. I've had to repair one of the Dallas ICs before. You have to dig out a dremel and bite down till you get to the metal then add some hook up wire. Unlike OP I chose to use rechargable batteries that used to be used for home wireless phones - they are the right voltage and often they supply a battery charger.

If you're lucky you can desolder the the old battery and use a couple of pin headers to get you back up and running. I do find it irritating some retro machines wont even boot without a working battery.