|If in doubt about the battery, replace it with a new one or a known good one.|
Some bioses can display the battery voltage in the current voltage, temp, and rpm readings. Usually a good battery reads 3 v or 3.3 v.
The battery must be installed so that the polarity of it is correct. In most cases the + must be visible when it is installed.
When you have removed the battery, then you have installed it, the first time you boot, you will get a "Cmos Checksum error" or similar message.
Go into the bios Setup and change the date and time to suit, and SAVE bios settings.
If you continue to get the "Cmos Checksum error" or similar message every time you boot, check the socket the battery is installed in.
- the contact that touches the top of the battery must not be bent such that it doesn't touch it. If it is bent, remove the battery and bend the contact towards the bottom or back of the socket, install the battery again
- if there is corrosion in the battery socket or on the underside of the top contact, you must remove it.
If all of the above does not help,
- make sure the Clear Cmos or similar jumper on the mboard is in the normal or run position, not the clear cmos position.
If it is in the clear cmos position, correct that, then set the time and date in the bios Setup.