Dell Precision M4600 CMOS Battery MR652 3V 200mAh Replacement

Dell Precision M4600 / M6600 — 3V Lithium CMOS Backup Battery (MR652)

This is a 3V, 200mAh lithium coin-cell battery that replaces the CMOS backup cell on Dell Precision M4600 and M6600 mobile workstations, plus Latitude X1 and E6320 series boards. It holds system settings, RTC clock data, and BIOS configuration when the laptop is off or unplugged. OEM part number MR652 is also sold under Dell references 0MR652, 313-032, and 313-020.

• Precision M4600 / M6600 and Latitude board compatibility: These platforms share a common CMOS circuit drawing from a single coin-cell socket. The cell supplies the SRAM and RTC rail independently of the main battery, so the voltage and connector form factor must match exactly — 3V, same footprint as MR652.
• Bench tested on actual hardware: We verified retention voltage under load on the CMOS rail. The cell held above 2.8V — the minimum the chipset requires to retain SRAM contents and keep the RTC ticking. BMS is not applicable; this is a non-rechargeable primary cell.
• Post-install BIOS step: After fitting the new cell, enter BIOS setup immediately and set the correct date and time, then save and exit. The RTC circuit resets to a factory default value on any power interruption — it does not self-correct once the new cell is installed.

BIOS clock resetting to 2000 after every power cycle on the M4600

The M4600 RTC circuit needs a minimum of 2.8V from the CMOS cell to retain clock data between power cycles. When the cell drops below that threshold, the chipset loses its time reference and falls back to a hardcoded default — typically January 1, 2000. This happens even if the laptop still boots normally from the main battery, because the CMOS cell and main pack are on separate rails. Replacing the MR652 cell and setting the correct date in BIOS resolves it immediately.

CMOS checksum error on boot after fitting a new coin cell

A checksum error immediately after a cell swap usually means the BIOS compared stored settings against what the SRAM now contains — and found a mismatch, because the SRAM cleared when the old depleted cell was removed. This is expected behaviour, not a faulty replacement cell. Enter BIOS setup, confirm or re-enter your settings, save, and exit. The checksum passes on the next boot once BIOS has written a fresh checksum against the newly saved configuration.