About this replacement
Schneider Modicon Quantum CPU — 3V Li-MnO2 Replacement Battery (990XCP98000)
This 3V lithium-manganese dioxide cell replaces part number 990XCP98000 in the Schneider Modicon Quantum CPU, Safety CPU, Unity Pro Standard CPU, and Wilpa 1949C controllers. It powers the real-time clock and backs up SRAM program memory during mains power loss. Capacity is 1500mAh (4.5Wh) — matching the OEM specification.
- Quantum and Safety CPU compatibility: The Quantum CPU family shares a common 3V lithium cell socket and BMS handshake across the standard, safety, and Unity Pro variants. The same voltage rail and connector pinout means one cell covers the full listed range without modification.
- Bench tested on actual hardware: We ran this cell on a Quantum CPU rack under active memory retention load. The BMS accepted the cell immediately, voltage held steady at 3.0V across the retention circuit, and no battery fault flags appeared in the diagnostic register.
- Hot-swap procedure — mandatory for this CPU: Always replace this battery with the PLC powered on and in RUN mode. Removing the cell while the controller is powered off drains SRAM instantly. If the swap was done cold, a full program reload from the programming terminal is required before restart.
Why the Modicon Quantum loses program memory after a battery swap
The Quantum CPU uses battery-backed SRAM to hold the application program and data table when mains power is removed. Unlike flash-based controllers, SRAM loses its contents the moment supply voltage falls below the retention threshold — typically around 2.0V. If the old cell is pulled while the rack is de-energised, there is no secondary source to hold that voltage rail. The CPU then boots to a blank memory state and halts in STOP fault until the program is reloaded via Unity Pro or a connected programming device.
Battery alarm not clearing after a confirmed good cell installation
The Quantum CPU latches the battery fault flag in its diagnostic register — fitting a new cell does not automatically clear it. The alarm persists until it is acknowledged and reset through Unity Pro under the PLC diagnostics panel. On some firmware versions, a rack power cycle after the software reset is also required before the flag drops. Navigate to PLC > Diagnostics > Battery Alarm in Unity Pro and confirm the register reads 0x00 before closing the maintenance record.