1756-BATM Allen Bradley PLC Replacement Battery 3.6V 38000mAh

Allen Bradley 1756-L6x Series — 3.6V Li-SOCl2 Replacement Battery (1756-BATM)

This is a 3.6V lithium thionyl chloride cell rated at 38000mAh, replacing OEM part 1756-BATM in Allen Bradley ControlLogix and CompactLogix PLCs. It fits the 1756-L6x, 1756-L6x Series A, 1756-L55M1x, 1756-L55M2x, and 29 additional 1756-series controller variants. The cell powers the real-time clock module and SRAM retention circuit during mains power loss.

• 1756-series compatibility: These controllers share a common battery bay connector and 3.6V SRAM retention rail. The BMS on each variant accepts the same cell footprint and chemistry — Li-SOCl2 is specified by Rockwell because of its flat discharge curve and low self-discharge rate over multi-year standby cycles.
• Bench tested on actual hardware: We ran this cell against a 1756-L63 in RUN mode. The controller recognised the cell immediately with no fault codes. SRAM retention voltage held above the 3.0V cutoff threshold throughout the test cycle, and the real-time clock maintained accurate time with no drift event recorded.
• Hot-swap protocol for 1756-series controllers: Never remove this battery while the PLC is powered off. Always replace the cell with the controller live and in RUN mode. SRAM is volatile — cutting power during a cold swap wipes the program from memory. If the PLC was off during the swap, reload the program from your programming device before restarting.

SRAM retention voltage threshold on the 1756-L6x

The 1756-L6x uses a dedicated SRAM retention circuit that pulls from the battery the moment mains power drops. Retention voltage must stay above 3.0V for memory to hold. A depleted Li-SOCl2 cell can sit at an apparent 3.2V under no load, then collapse immediately under the SRAM draw — giving a false reading on a handheld meter. The only reliable test is to check the battery alarm status in RSLogix 5000 or Studio 5000 under the controller diagnostics tab, not with a multimeter.

Battery alarm not clearing after a confirmed good installation

The 1756-series battery alarm does not reset automatically when a new cell is fitted. The controller latches the alarm in firmware until it is manually cleared. Open Studio 5000 or RSLogix 5000, navigate to Controller Properties, select the General tab, and click the reset button next to the battery fault indicator. If the alarm returns within 24 hours of clearing, verify the cell is seated fully and the connector is locked — a partially seated cell reads as absent to the controller diagnostics.