Compaq DESKPRO 5233MX CMOS Compatible Battery 3.6V 2700mAh

Compaq DESKPRO 5233MX — 3.6V Li-MnO2 Replacement Battery

This is a 3.6V, 2700mAh lithium manganese dioxide cell that replaces the CMOS backup battery on the Compaq DESKPRO 5233MX motherboard. It holds system time, date, and BIOS configuration when the machine is off or unplugged. When this cell depletes, the board loses its settings on every power cycle.

• DESKPRO 5233MX motherboard fit: The 5233MX uses a barrel-style 3.6V Li-MnO2 cell to power the RTC and CMOS SRAM. Voltage, physical dimensions (60.55 × 18.50 × 18.35mm), and connector type must all match — a standard CR2032 coin cell will not substitute here.
• Bench tested on actual hardware: We ran this cell against a 3.6V RTC circuit and confirmed stable float voltage with no BMS-induced drop. Open-circuit voltage held within spec across the full test window.
• Swap timing on the DESKPRO 5233MX: Replace this cell with the machine powered on where possible. Removing the battery while the board is completely de-energised clears CMOS — you will need to re-enter BIOS settings manually on next boot.

Why the DESKPRO 5233MX loses date and BIOS settings after every shutdown

The RTC and CMOS SRAM on this board draw continuous low current from the backup cell whenever mains power is absent. Once the cell drops below roughly 3.0V, retention fails and the board resets to factory defaults on each power cycle. A depleted cell often still reads a surface voltage above 3.0V under no load — that reading is misleading. Under the small but constant RTC draw, the cell collapses and CMOS clears. Replacing the cell is the only fix; reseating or cleaning the holder changes nothing if the cell itself is exhausted.

New cell installed but DESKPRO 5233MX still showing wrong date and time

A fresh Li-MnO2 cell ships at storage voltage, which can sit slightly below the board's expected 3.6V until it equilibrates under light load. If the date and time are still wrong after fitting the new cell, the CMOS was cleared during the swap and the RTC has no stored values to recover. Boot into BIOS setup, set the correct date and time manually, and save before exiting. Confirm the board holds those values through a full power-off cycle — if it does, the new cell is seated and functioning correctly.