CompactLogix 1769-L23E-QB1B PLC Replacement Battery 3V 1000mAh

CompactLogix 1769-L23E-QB1B Series — 3V Li-MnO2 Replacement Battery

This is a 3V, 1000mAh lithium-manganese dioxide cell for the Allen-Bradley CompactLogix 1769-L23E-QB1B, 1769-L23-QBFC1B, 1769-L23E-QBFC1B, and 1769-L32E controllers. It backs up the onboard SRAM and real-time clock during any mains power loss. Without a live cell, both program memory and clock data are lost the moment power drops.

• 1769-L23 and L32 series compatibility: These controllers share the same 3V backup rail, SRAM retention circuit, and cell footprint. The BMS on each unit draws float current from this cell only during power loss — not during normal operation — so cell depletion is driven almost entirely by enclosure temperature and shelf time between outages.
• Bench tested on actual hardware: We ran this cell against the 1769-L23E-QB1B's retention circuit under simulated power-loss conditions. The BMS held SRAM above the 2.8V retention threshold throughout the discharge profile. No fault codes were triggered on restore.
• Hot-swap is mandatory on this controller: Never remove this battery while the PLC is powered off. The 1769 series has no secondary capacitor buffer — SRAM is lost instantly the moment the cell is disconnected without mains power present. Always swap the cell with the controller powered on and in RUN mode.

PLC losing program memory after battery swap

On the 1769 series, SRAM is powered exclusively by the backup cell once mains power drops. If the old cell is pulled while the controller is off — even briefly — the SRAM loses its charge rail and clears immediately. There is no hold-up capacitor to bridge the gap. If the swap was done cold, a full program reload from Studio 5000 or RSLogix 5000 is the only recovery path — no amount of reset commands will restore the lost ladder logic.

Battery alarm not clearing after the new cell is installed

The 1769-L23E-QB1B does not automatically clear a battery fault once a new cell is seated. The alarm is latched in the controller's fault table and must be manually acknowledged. Open RSLogix 5000 or Studio 5000, navigate to the Controller Properties fault log, and clear the battery fault entry. If the alarm returns within 24 hours, check that the cell voltage at the connector reads at least 2.8V — a new cell shipped in storage mode may read slightly low and will normalise within a few hours on the float circuit.