Asus Eee PC 1008HA CMOS Battery 3V 40mAh Lithium 0108

Asus Eee PC 1008HA / 1005HA Series — 3V Lithium CMOS Backup Battery (0108 / ML1220-2E2EOX)

This is a 3V, 40mAh lithium coin cell that keeps the BIOS settings and real-time clock alive on the Asus Eee PC 1008HA and 1005HA series when mains power is removed. It sits on the motherboard and backs the CMOS SRAM and RTC circuit continuously. When the original cell depletes below the 2.8V retention threshold, the system loses the date, time, and stored hardware configuration on every power cycle.

• Eee PC 1005HA and 1008HA compatibility: Both models share the same ML1220-footprint socket and connector on their respective motherboards. The cell voltage rail, contact orientation, and BMS-free circuit draw are identical across the series, so one part number covers both.
• Bench tested on actual hardware: We verified open-circuit voltage at 3.0V before shipment and confirmed the cell holds retention voltage under a simulated CMOS SRAM standby load without drop-off. No BMS is present — this is a passive lithium cell, and draw from the RTC circuit is in the microamp range.
• Post-installation clock correction: After fitting this cell, enter the BIOS immediately and set the correct date and time, then save and exit. The RTC circuit powers down to default values the moment the old cell is removed, and the new cell will hold whatever timestamp you write — not auto-correct it.

BIOS clock resetting to 2000 after every power cycle on the Eee PC 1005HA / 1008HA

The RTC circuit on these Eee PC motherboards draws a continuous microamp-level current from the CMOS cell to hold the clock register and system settings in SRAM. Once the cell drops below roughly 2.8V, it can no longer sustain that standby load, and the SRAM clears every time mains power is cut. The system then boots with a hardcoded default timestamp — typically January 1, 2000 — because that is the value baked into the BIOS ROM as a fallback. Replacing the coin cell and writing the correct date in BIOS setup stops the reset loop immediately.

CMOS checksum error on boot after fitting the new cell

A checksum error on first boot after a cell swap is normal — it means the BIOS detected that the stored configuration data no longer matches its own checksum, usually because the SRAM cleared completely during the swap. This is not a sign of a faulty replacement cell. Enter BIOS setup, confirm or restore your settings, set the correct date and time, then save and exit. The checksum recalculates on save, and the error will not appear on subsequent boots as long as the new cell holds above 2.8V.