That is the RTC "real Time Clock" battery. It maintains all your date and time as well as other settings. That way, even if you change the main batteries, all data and setting remain. Check on here to see how to change it.
We have a chance to guarantee our right to repair electronic
equipment—like smartphones, computers, and even farm equipment. This is a once-in-a-generation
chance to protect local repair jobs—the corner mom-and-pop repair shops that
keep getting squeezed out by manufacturers.
Join the cause and tell your state representative to support Right to Repair. Tell them you believe repair should be fair, affordable, and accessible. Stand up for your right to repair!