Thanks. It seems pretty straightforward to connect a backup battery: disconnect the 150 Ohm resistor between pin 4 and 3.3v, and connect a battery between pin 4 and GND. Now I need to get a battery & holder (maybe from an old PC motherboard).
I have also timed this process..it seems you need to wait at least 5 minutes for a decent number locked, the longer (20 minutes>) the better...must be a faster/better way?
Thanks, I already bought one. I will probably connect it this weekend.