Medion MD42200 CMOS Replacement Battery 3V 200mAh

Medion MD42200 — 3V Lithium CMOS Backup Battery

This is a 3V lithium coin cell battery rated at 200mAh (0.6Wh), sized at 30.10 x 20.12 x 4.12mm. It fits the Medion MD42200 motherboard and powers the RTC circuit and CMOS SRAM when mains power is disconnected. Replace it when the board loses time, forgets BIOS settings, or throws a checksum error on boot.

• MD42200 motherboard fit: The MD42200 uses a non-standard oblong lithium cell rather than a round CR2032. The connector and footprint on this board require the exact 30.10 x 20.12 x 4.12mm form factor — a standard coin cell will not seat correctly in the retention clip.
• Bench tested on actual hardware: We measured open-circuit voltage at 3.0V and confirmed the cell holds above the 2.8V CMOS retention threshold under the low-draw RTC load. The BMS on this non-rechargeable cell is passive — no handshake required, voltage delivery is immediate on contact.
• Post-install clock correction: After fitting this cell, enter BIOS immediately and set the correct date and time, then save and exit. The RTC circuit resets to a default value on every power interruption — the new cell will hold whatever date and time you set, but it cannot recover a timestamp the board never stored.

BIOS clock resetting to 2000 after every power cycle

The MD42200 RTC circuit draws from the CMOS cell continuously whenever mains power is off. When cell voltage drops below 2.8V, the SRAM loses retention and the clock falls back to its firmware default — typically January 1, 2000. A cell measuring 2.9V at rest can still fail this test under the sustained microamp draw of a long power-off period. Replacing the cell and then setting the correct time in BIOS resolves this permanently.

CMOS checksum error on boot after fitting a new cell

A checksum error after a cell swap usually means the BIOS detected that all stored settings were lost during the replacement — not that the new cell is faulty. When the old cell was removed, CMOS SRAM lost power and every setting was wiped, including the checksum the BIOS uses to verify its own configuration. Enter BIOS setup, restore any custom settings, set the correct date and time, then save and exit. The error will not reappear as long as the new cell stays above 2.8V.