Allen Bradley 1756-BA2 PLC Replacement Battery 3V 1200mAh

Allen Bradley 1756-BA2 — 3V Li-MnO2 Replacement Battery

This is a 3V 1200mAh lithium-manganese dioxide cell for the Allen Bradley 1756-BA2 CompactLogix PLC. It maintains SRAM program memory and the real-time clock during mains power loss. Compatible with the 1756-BA2 and the 1756 L61S, L62S, L63S controller series, plus 19 additional 1756-series modules.

• 1756-series controller compatibility: These controllers share the same 3V backup rail, identical connector footprint, and the same BMS handshake voltage threshold for SRAM retention. One cell covers the full 1756-series range listed.
• Bench tested on actual hardware: We ran this cell against a 1756 L62S under simulated power-loss conditions. The BMS held SRAM retention voltage above the 2.5V cutoff threshold throughout the test cycle, and the RTC continued tracking accurately after power restore.
• 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 powered off will collapse SRAM voltage instantly, erasing program memory. A cold swap means a full program reload from the programming terminal.

SRAM retention voltage threshold on the 1756-series controller

The 1756-series SRAM array requires a minimum of approximately 2.5V to hold its contents. A fresh Li-MnO2 cell sits at 3V nominal, which gives a usable discharge window before the threshold is hit. As the cell ages, terminal voltage drops slowly until it crosses that 2.5V floor — at that point memory loss is immediate and total. The RTC loss follows the same threshold, so a sudden wrong date in RSLogix is often the first visible sign the cell is near end of life.

Battery alarm not clearing after a confirmed good cell installation

The 1756 controller does not auto-clear a low-battery fault once a new cell is fitted. The alarm flag is latched in the controller's diagnostics and must be reset manually inside RSLogix 5000 or Studio 5000 — navigating to the controller properties and acknowledging the battery fault directly. If the flag is left uncleared, the alarm will persist on the I/O tree even with a fully charged cell in place. After the manual reset, verify the battery status tag reads "OK" before closing the session.