Check the listing for details. 2x CMOS BIOS Battery for Dell E5420 E5430 E5440 E5450 E5470 E5480 Reserve Backup. Condition: New. Listed at 6.64 USD. 2x Brand New Dell Real Time Clock Battery (RTC) CMOS BIOS BACKUP Reserve Weight 0.03Volts 3VChemistry LithiumDimensions 23mm x 23mm x 3.0mmDetails 3 Volt Lithium Battery Will Fit Dell Latitude Series -- Dell Latitude E5250 E5420 E5430 E5440 E5450 E5470 E5480 Always got wrong date and error message when you turn on your laptop? Even the Windows XP can't be loaded correctly?? (Windows XP can't be loaded correctly when the Date setting is no sense, this could happen when the CMOS battery voltage is low). Then it is time to change your CMOS RTC coin battery! Every laptop has a small coin cell battery to power the BIOS chip to keep the date, and other internal settings effective. Without these cmos batteries or a dead cmos battery these internal setting will not function. CMOS RTC battery should be replaced every few years (typically 3-4 yrs).