One day the inevitable happens on your PC, the CMOS battery fails. This can be diagnosed as the usual cause of the computer needing to have the time and date to be re-entered every time the computer loses power. If your laptop battery is dead and you are running it off the charger, you will have this annoying problem every time you unplug it. In this Instructable, I will be focusing particularly on laptops. In this case an IBM Thinkpad R40. In many laptops, you can access the CMOS battery from some of the access panels on the bottom. On the Thinkpad R40, you can replace the CMOS battery and the fan from under the keyboard. Before you do anything, remove the main battery, which is easily removed at the bottom of the laptop by the movement of one lever and with one finger in the slot, it will fall out. The keyboard is easily unfastened by the removal of the two screws underneath the white markers (note I have put these white markers on the photo) on the photograph of the underside of the computer. The keyboard is then gently pried out by the insertion of a small flat bladed screwdriver on one side and then the other. Be careful that you don't lift it more than an inch or so as there is a ribbon cable underneath that can be damaged. Gently pull up the bottom of the keyboard once it is free and rest it against the screen which should be rested flat. The CMOS battery holder can be seen in the last photo. The battery was gently pried up and the connector removed.

Step 1: Items Needed to Do the Job.

1) Long nose pliers

2) Electrical Tape

3) Small Phillips Screwdrivers

4) (1) 2032 Battery

5) Small flat bladed screwdriver

6) Soldering gun.

7) Knife

8) Solder

Step 2: Finding Out Where the CMOS Battery Is Kept in Your Computer.

In this picture you can see the little holder that holds the CMOS battery with the battery taken out.

Step 3: Taking Out the Battery and Determining If It Can Be Replaced

The battery was taken out and the plastic covering was cut with a knife. It was determined that the battery was an easily obtainable 2032. Both the negative and positive terminals are spot welded onto the battery surface.

Step 4: Gently Twisting the Taps Off the Old Battery

Gently pry the terminals off the old battery with a rolling motion using a pair of needle nose pliers. Do this gently to avoid wrecking the terminals.

Step 5: Solder the Tabs Onto the New Battery.

Roughen up the positive and negative surfaces of the new battery with steel wool or a file. Solder the red wire terminal to the + terminal of the battery and the black to the - terminal of the battery with electronic solder preferably using a soldering gun. I tried using a 25 watt soldering iron but it wasn't enough heat to melt the solder sufficiently.

WARNING: WEAR SAFETY GOGGLES OR A FULL FACE VISOR WHEN DOING THIS AS THESE BATTERIES CAN EXPLODE IN YOUR FACE IF TOO MUCH HEAT IS APPLIED.

Step 6: After Soldering the Terminals Onto the New Battery, Wrap in Electrical Tape.

After soldering the terminals onto the new battery, wrap in electrical tape and install in computer. I put the original black shrink wrap on the new battery and wrapped that in electrical tape for extra insulation.