About this replacement
Dell Alienware M11X Series — 3V Lithium CMOS Replacement Battery (P06T)
This is the CMOS/RTC backup cell for the Dell Alienware M11X, M11X R1, M11X R2, M15X, and related models. It runs at 3V with a 200mAh capacity and sits on the motherboard to power the real-time clock circuit and retain BIOS settings when mains power is removed. When this cell depletes below the 2.8V retention threshold, the system loses its clock and stored configuration on every power cycle.
- M11X and M15X motherboard compatibility: These models share the same CMOS socket footprint and OEM part number P06T. The cell dimensions — 25.20 x 20.32 x 4.80mm — match the motherboard housing directly. No adapter or modification is needed.
- Bench tested on actual hardware: We measured open-circuit voltage before shipping. Each cell reads at or above 2.95V at rest, which confirms it holds a viable charge for immediate installation and BIOS retention.
- Post-install clock correction: After fitting this cell, enter BIOS setup immediately and set the correct date and time before saving and exiting. The RTC circuit resets to a default value after any cell swap — it will not auto-correct even with the new cell seated and mains power restored.
BIOS clock resetting to 2000 after every power cycle
The RTC circuit on the M11X motherboard requires a minimum of 2.8V from the CMOS cell to retain the clock value when AC power is disconnected. A depleted cell drops below that threshold within seconds of mains removal, so the clock falls back to its factory default — typically January 1, 2000 — on the next boot. This is not a firmware fault or a Windows issue. Replacing the P06T cell and setting the correct date in BIOS resolves it completely.
CMOS checksum error on boot after fitting a new coin cell
A checksum error immediately after a cell swap usually means the BIOS lost all stored settings before the new cell made contact — common when the old cell was fully depleted and there was a gap between removal and installation. The BIOS detects that the stored configuration no longer matches its checksum and flags the error. Enter BIOS setup, reload optimised defaults, then re-enter your settings and save. Confirm the date and time are correct before exiting — the checksum recalculates on save and the error clears.