The back-up lithium battery on the logic board of the Macintosh computer may have reached the end of its lifespan and needs to be replaced. The battery provides power to the logic board to save the control panel settings when you turn the machine off or interrupt power to it losing the settings. When the machine is restarted the power supply continues to run and control panel settings will not be lost.
With certain Macintosh models, a low battery results in a black screen (no video). For more information on this issue, please see the following Tech Info Library article:
Article 20328: "
Macintosh Computers: Low Battery Can Cause No Video"
Any authorized service provider should be able to replace the dead battery. Since the battery is located on the logic board of the Macintosh, we suggest that users not attempt to replace the battery themselves. The logic board can be easily damaged by static electricity, incorrect handling, or an incorrectly inserted battery.