Some users may experience a problem in which basic settings in the computer seem to revert themselves, especially on older computers.
Apple Discussions poster Katrina Wittich writes:
"I have an old powerbook G4 and lately the date/time has reset itself several times back to Dec 1969. I did just change to a new battery, so maybe that has something to do with it."
In addition to the system's date, settings such as the speaker volume can also change. Although users may suspect the main battery or something with the main power supply to be causing the problem, in general when these settings reset themselves, it indicates the backup battery on the computer's motherboard is going bad.
In all Macs, there is a small battery on the motherboard that provides a constant charge to the CMOS/PRAM, which maintains the PRAM settings when the computer completely loses all power (batteries unplugged and AC power disconnected). This battery can look like a small C-cell, or like a flat coin-like battery and can either be directly mounted to the motherboard, or stuck to it and connected via a wire.
The batteries are not rechargeable, and serve as a backup in case the main power is lost to the computer. However, as is the case with any battery, these can lose their charge over time and users can have dead ones in their computers without knowing it, especially in the case of laptop owners who've either kept the main battery in or kept it plugged into the AC power.
There are two recommended options for users to overcome this problem.
Workaround: Use a network time server Mac OS X has the ability to set the time automatically via a network time server. When enabled this feature should check the time periodically if the computer is left on, or when the computer is rebooted. To set a time server, open the "Date & Time" system preferences and in the "Date & Time" tab, check the box to set the date and time automatically. Then choose a time server from the drop-down menu ("time.apple.com" is the default). Alternative time servers can be manually entered in to the time server list.
Fix: Replace the logic board battery For users who are not always connected to the internet who restart the computer occasionally, the only option would be to replace the battery. There are several sources online (http://www.ifixit.com/, http://www.apple.com/support/programs/ssa/) on how to access the battery on the motherboard if users wish to repair the computer themselves, or users can take the computer to an Apple-authorized service provider for battery replacement.