Dell Inspiron 8500 CMOS Replacement Battery W0124 7.2V

Dell Inspiron 8500 / 8600 Series — 7.2V Ni-MH CMOS Backup Battery (W0124)

This is the CMOS backup battery for the Dell Inspiron 8500, 8600, 8600c, and Precision M60. It runs at 7.2V with a 40mAh capacity and uses Ni-MH chemistry. Its sole job is to power the RTC circuit and hold BIOS settings when the laptop is unplugged or switched off.

• Inspiron 8500, 8600, 8600c, and Precision M60 fitment: These models share the same CMOS circuit board connector, retention voltage threshold, and physical mounting bay — one cell covers all of them without modification.
• Bench tested on actual hardware: We ran this cell against the CMOS circuit under load and confirmed stable voltage output above the 2.8V minimum retention threshold that the Inspiron BIOS requires to keep settings intact between power cycles.
• Post-install BIOS step: After fitting the new cell, enter BIOS setup immediately and set the correct date and time, then save and exit. The CMOS cell powers the RTC circuit, so any gap between removing the old cell and powering up resets the clock to a factory default that must be manually corrected.

BIOS clock resetting to 2000 after every power cycle on the Inspiron 8500

The Inspiron 8500 RTC circuit draws continuously from the CMOS cell whenever mains power is absent. When the cell drops below 2.8V, the RTC loses retention and the BIOS resets the clock to its default date — typically January 1, 2000. This happens every single power cycle because the cell can no longer sustain the minimum voltage. Replacing the W0124 cell restores continuous RTC power and stops the reset loop. After fitting, set the correct date in BIOS and save before closing the lid.

CMOS checksum error on boot after fitting the new cell

A checksum error on first boot after a cell swap means the BIOS compared stored settings against an empty or default CMOS state and found a mismatch. This is expected when the old cell was fully depleted — SRAM contents are gone and the BIOS flags the discrepancy. Press F1 or the key your BIOS prompts, enter setup, verify all settings, then save and exit. A clean save writes a fresh checksum and the error will not return on the next boot.