Apple IMac - Logic Board Battery

Troubleshooting Logic Board Battery/ - 26
Logic Board Battery
The battery on the logic board controls the stored system settings,
such as date and time. It is important to note that the battery does
not affect power at startup.
The battery should be replaced if your system loses date and time
settings.
Note : The iMac uses a lithium battery which must be disposed of in
accordance with hazardous waste regulations.