Fixes your Checksum Error upon Laptop's bootup 2PJ Maintains your date and time. CMOS batteries have a shelf life. Some point it gets drained and non functioning. This is not the Laptop's Main Battery On stock! Check Photo for your reference Brand New/ Tested prior to Shipping Disclaimer: It will come in different wrappings ( blue/black yellow) We have different kinds. #cmos #cmosbattery #realtimeclock #shipsin24hours