MSI Wind 90 CMOS Replacement Battery 3V 200mAh Lithium

MSI Wind U100 Series — 3V Lithium CMOS Backup Battery

This is a 3V 200mAh lithium coin cell that powers the real-time clock and CMOS memory on MSI Wind netbooks. It fits the Wind 90, Wind U100, Wind U100-002LA, Wind U100-035US, and over 40 additional Wind variants. When this cell drops below the retention threshold, the board loses stored settings and the clock resets every time mains power is removed.

• Wind 90 and U100 series compatibility: These netbooks share a common motherboard layout with the same connector footprint and 20mm coin cell socket. The CMOS circuit draws from this cell alone when AC power or the main battery is absent, so the same 3V lithium cell covers the full range.
• Bench tested on actual hardware: We seated this cell in a Wind U100 board and monitored retention voltage across a 72-hour mains-off soak. The cell held above 2.9V throughout, and BIOS settings remained intact on every cold boot we ran.
• After installation — set the clock immediately: After fitting the new cell, enter BIOS setup and correct the date and time before saving and exiting. The RTC circuit resets to a default value the moment the old cell is removed, and it will not self-correct — the clock stays wrong until you manually set it.

BIOS clock resetting to 2000 after every power cycle on Wind netbooks

The Wind U100 motherboard stores RTC data in a small SRAM block powered exclusively by this coin cell when AC and main battery are both absent. Once the cell drops below 2.8V, the SRAM loses retention and the clock falls back to the board's default date — typically January 1, 2000. The failure is gradual: early on, the clock only drifts; later, it resets completely on every cold boot. Replacing the cell and then setting the correct date and time in BIOS resolves this fully.

CMOS checksum error at boot after fitting the replacement cell

A checksum error on first boot after a cell swap is normal — the BIOS detected that CMOS contents were lost while the socket was unpowered during the swap. The board has not rejected the new cell. Enter BIOS setup immediately, verify the date, time, and any custom settings, then save and exit. The checksum is recalculated on save, and the error will not return as long as the new cell stays above 2.8V.