FYI and sort of related.
System 3 CPU boards as shown in photo above use a DS1210 to control the memory and switch the coin cell over to powering the RAM during machine power down. This seemed to be the first IC (U6) taken out by battery leakage.
The Dallas Semiconductor DS1210's (and DS1210+) used by the System 3s are no longer made.
Replacement is the MXD1210 --> Full part number MXD1210CPA+.
Yes, Lithiums do leak but not as rapidly as NiCads.