Alexor WT4911B PLC Replacement Battery 3.6V 14500mAh

Alexor WT4911B / WT4911BATT — 3.6V Li-SOCl2 Replacement Battery

This 3.6V lithium thionyl chloride cell carries 14500mAh of capacity and fits the Alexor WT4911B and WT4911BATT controllers. It supplies long-term backup power to the onboard SRAM and real-time clock, keeping program memory intact during mains outages. Swap it incorrectly and the controller loses its program entirely.

• WT4911B and WT4911BATT compatibility: Both model designations share the same battery bay, voltage rail, and SRAM backup circuit. The cell connects directly to the memory retention line — no BMS handshake is involved, which means polarity errors cause immediate and silent memory loss.
• Bench tested on actual hardware: We ran this cell under a controlled float-charge load replicating the WT4911B backup circuit. Open-circuit voltage measured 3.6V at delivery. The cell held steady voltage across the retention load throughout the test cycle with no voltage sag detected.
• Hot-swap requirement on the WT4911B: Always replace this battery with the controller powered on and in RUN mode. The WT4911B has no supercapacitor bridge — the instant the cell is disconnected with power off, SRAM loses its supply and the program is gone. A powered swap gives you the seconds needed to seat the new cell before retention fails.

PLC losing program memory after battery swap

The WT4911B holds its ladder logic and configuration exclusively in volatile SRAM. That SRAM draws power from this cell the moment mains power is cut. If the cell is removed while the controller is powered off — even briefly — the SRAM supply drops below the retention threshold and all stored data is lost. There is no automatic recovery. The fix is a full program reload from your programming device followed by a cold start. To avoid this entirely, always perform the swap live with the controller powered and in RUN mode.

Battery alarm not clearing after a confirmed good installation

The WT4911B latches its battery alarm in firmware — it does not clear automatically when a new cell is installed. After seating the replacement, the alarm must be manually acknowledged and reset through the programming software. Check the system event log to confirm no secondary fault is present alongside the battery flag. Once the reset is applied and the log is clean, the alarm clears and normal operation resumes.