My CMOS battery was dying on my Sony Vaio PCG-GR390 laptop. It took me a moment to realize how to get into the innards. Here explains how to replace CMOS battery or other parts exposed containing keyboard and maybe fan.

Instructions

1. Obtain a battery. These are difficult to look for decent costs. I finally found one by doing a search for "2/V15H". I consider 4D Electronics was one but they did not have part and required $20 plus $10 sending.

2. Detach all power sources AC adapter and the main battery also.

3. Take out strip above keyboard. That has speakers, and model number. First take out rubber button above F3 key and below the screen. I utilized a little knife but a little screwdriver will work, too. Second, take out head screw below button. Lastly, push on the right end of strip to release "hooks" holding that end and center of the strip, lift the strip about 1/2in, and fold the strip back against screen. You do not want to remove cables or connectors.

4. Take out keyboard. There is a little head screw above F8 key. Take out that and keyboard can then be folded down over Touchpad. If you are changing keyboard, you do not want to detach it.

5. Change the battery. CMOS battery is around in center of PC case under keyboard. It is most likely labeled 2/V15H, 2.4V, 15mAh. You can unhook old battery connector and hook up new battery, leaving old battery in PC. The new one can be installed on top of old battery.

6. Reconstruct. Reconnect the keyboard, its screw, strip with speakers, its screw, battery, and AC connector and you must be ready to boot. You will have reset CMOS memory in process so all will revert back to default settings. You can reset clock before booting Windows or wait and do this after Windows is booted.