Thinkpad T420 - CMOS battery replacement

A long time ago I bought several Lenovo Thinkpad T420 laptops (used of course). But my wife’s laptop gave her the dreaded error (after power loss):

Real Time Clock Error - Check Date and Time settings.
Press Esc to continue or F1 to enter Setup.

Finally I got fed up with it, so I swapped out her old CMOS backup battery with a new one. Then I also did the same for my other T420’s.

iFixit has a good write up on replacing the keyboard on a Thinkpad T420, which can be followed until “Step 6 - Disconnect the keyboard”. At step 6 in the 3rd picture, you can see a yellow, shrink wrapped, circular item. That is the CMOS backup battery. It can be easily be unplugged and taken out.

You can buy a new one on ebay starting from $7.99, but you can also try to replace it yourself with a CR2032 button cell battery. I bought an 8-pack of CR2032 batteries for 0.99 euro and grabbed a sharp/thin knife, electrical tape and pliers. Essentially these were the steps:

• slice open the yellow plastic
• remove the battery from the plastic
• use the pliers to remove the leads from the battery
• reapply the leads to the new battery and keep them in place with eletrical tape
• reapply the yellow plastic case and use electrical tape to close it up

After that the laptop can be assembled again using the iFixit manual.

P.S. Apparently Joey deVilla also noticed the DIY option, but he had already ordered the replacement battery online for his T430s