Asus Eee PC Flare R052C CMOS Battery 3V 200mAh Lithium

Asus Eee PC Flare R052C — 3V Lithium CMOS Backup Battery

This is a 3V 200mAh lithium coin cell that powers the real-time clock and CMOS SRAM on the Asus Eee PC Flare R052C motherboard. It keeps BIOS settings and date/time intact when the laptop is unplugged or the main battery is removed. When this cell drops below retention voltage, the system loses its clock and stored configuration on every power cycle.

• Eee PC Flare R052C motherboard fit: The R052C uses a standard 20mm coin cell socket wired directly to the RTC and CMOS SRAM circuits. This replacement matches the 20.00 × 20.00 × 3.80mm footprint and 3V nominal voltage that circuit expects.
• Bench tested on actual hardware: We measured open-circuit voltage at dispatch and confirmed the cell holds above 3.0V. The CMOS circuit draws in the low-microamp range, so a fresh cell at full capacity will retain settings across extended mains-off periods.
• After-swap BIOS step: After installing, enter BIOS setup and manually set the correct date and time, then save and exit. The RTC circuit resets to a default value during the swap — it cannot self-correct without a manual entry after the cell is seated.

BIOS clock resetting to 2000 after every power cycle on the R052C

The RTC circuit on the R052C requires a minimum of 2.8V from the CMOS cell to retain clock data. Once the cell drops below that threshold, the clock resets to a default date — usually January 1, 2000 — every time mains power is interrupted. This happens even if the laptop still boots and runs normally, because the main battery does not back the CMOS circuit on this platform. Replacing the coin cell and resetting the date in BIOS resolves it immediately.

CMOS checksum error appears on boot after fitting a new cell

A checksum error on first boot after a cell swap means the BIOS detected that stored settings no longer match their checksum — normal when the CMOS was fully discharged before replacement. The fix is straightforward: enter BIOS setup, reset to defaults, set the correct date and time, then save and exit. If the error persists after saving, check that the coin cell contact spring is making clean contact with the cell's positive face. A bent or oxidised spring holds the cell at an angle and breaks the circuit intermittently.