Modicon 884 PLC Replacement Battery 3V 900mAh B9625T

Modicon 884 / 984X Series — 3V Li-MnO2 Replacement Battery (B9625T)

The B9625T is a 3V lithium manganese dioxide cell rated at 900mAh. It fits the Modicon 884, 984X, 984X-008, and ASC11/BASIC series Programmable Logic Controllers. This cell maintains the real-time clock and backs up SRAM program memory during mains power loss.

• 884 and 984X platform compatibility: These controllers share the same B9625T socket, voltage rail, and SRAM retention circuit. The 3V cell feeds the memory backup directly — no BMS handshake is involved, making cross-model fit straightforward across this product line.
• Bench tested on actual hardware: We ran this cell against the B9625T specification and confirmed stable 3V output under the low-current standby draw typical of Modicon SRAM retention circuits. Voltage held within tolerance across the test window.
• Hot-swap procedure — critical for this controller: Always replace this battery with the PLC powered on and in RUN mode. Removing the cell while the controller is off will immediately clear SRAM. If that happens, a full program reload from the programming device is required before the PLC can return to service.

Why the Modicon 884 loses program memory after a battery swap

The 884 uses volatile SRAM for program and data storage. That memory is held entirely by the B9625T cell when mains power is absent. The moment the cell is disconnected — even briefly — SRAM loses its supply voltage and all stored data is erased. There is no internal capacitor or secondary hold-up circuit to bridge the gap. Swap the cell only while the PLC is live and the memory bus is powered from the mains supply.

Battery alarm not clearing on the 984X after a confirmed good installation

The 984X does not auto-clear the low-battery flag when a new cell is fitted. The alarm is latched in the controller's diagnostic status register and must be reset manually through the programming software. Connect your programming terminal, navigate to the diagnostic or status word for battery condition, and force a reset of that bit. Until that step is done, the alarm will continue to show regardless of the new cell's actual voltage.