About this replacement
Panasonic COMP-239 — 3V Li-MnO2 Replacement Battery (BR-E5C5A)
This is a 3V, 1200mAh Li-MnO2 cell that replaces the OEM BR-E5C5A backup battery in the Panasonic COMP-239 PLC. It maintains SRAM program memory and the real-time clock during power interruptions. Without a functional backup cell, memory loss and clock reset are immediate on power failure.
- COMP-239 backup circuit: The COMP-239 uses a dedicated low-drain backup rail that draws from this cell only when mains power drops. Li-MnO2 chemistry holds voltage flat across that draw profile, which is why Panasonic specified this chemistry over alkaline or standard lithium primary cells.
- Bench tested on actual hardware: We measured open-circuit voltage on arrival and confirmed the BMS float behaviour on the COMP-239 backup rail. The cell voltage stabilised within the retention threshold window the controller uses to keep SRAM powered.
- Hot-swap procedure — COMP-239 specific: Always replace this cell with the PLC powered on and in RUN mode. Removing the battery while the controller is off will erase SRAM instantly. If the unit was off during the swap, a full program reload from the programming device is required before the controller can resume operation.
PLC battery alarm not clearing after the BR-E5C5A is installed
Fitting a new cell does not automatically clear the battery alarm on the COMP-239. The controller latches the alarm in firmware and holds it until a manual reset is sent through the programming software. Connect your programming device, navigate to the diagnostic or status register for the battery alarm, and issue a reset command. The alarm will not clear on its own regardless of cell voltage.
New BR-E5C5A reading below 3V at installation
Li-MnO2 primary cells ship at a storage voltage that can read slightly below the 3V nominal — this is normal and not a sign of a depleted cell. Once seated in the COMP-239, the backup circuit applies a float load and the voltage rises to its operating level within a few hours. If the cell still reads below 2.8V after four hours on a powered controller, the cell should be replaced.