The PRAM backup battery in the PowerBook G4 is a Panasonic CGL-3032 3.6v lithium-ion cell. Unlike most desktop Mac backup batteries, it is a RECHARGEABLE cell. That's one reason it's more expensive than your typical little LiI battery. Since it's rechargeable, you can't simply measure the cell voltage to determine if the battery is worn out. The little PCB assembly contains the charge control circuitry. The "3032" nomenclature refers to the size: 30 mm in diameter by 3.2 mm thick. A similar cell is available from other manufacturers, typically in China. Look for LIR-3032. Specs for the Panasonic CGL-3032 Specs for LIR-3032