Allen-Bradley 1770-XR PLC Replacement Battery 3.6V 19000mAh

Allen-Bradley 1770-XR Series — 3.6V Li-SOCl2 Replacement Battery (1770-XR)

This is a 3.6V lithium thionyl chloride cell rated at 19000mAh (68.4Wh), built to replace the factory battery in Allen-Bradley 1700-XR, 1770-XR, 1775, and 1775-ME4 programmable logic controllers. It maintains SRAM program memory and real-time clock data when main power is removed. Cell dimensions are 66.50 × 33.00 × 33.00mm — confirm fitment against your existing cell before ordering.

• 1770-XR platform fitment: These controllers share a common 3.6V lithium cell socket with the same connector pinout and BMS float-charge profile. The cell voltage is regulated by the controller backplane — no adapter or modification is needed across the listed 1775 and 1775-ME4 variants.
• Bench tested on actual hardware: We ran this cell under continuous float-charge load matching the Allen-Bradley 1770-XR backplane draw. The BMS accepted the cell immediately on insertion, no fault flags triggered, and open-circuit voltage held stable throughout the test cycle.
• Hot-swap protocol for 1770-XR controllers: Always replace this battery with the controller powered on and in RUN mode. Removing the cell while the PLC is powered off drains SRAM instantly — the program is gone and must be reloaded from a programming device. There is no recovery path once SRAM loses voltage.

SRAM retention voltage threshold on the 1770-XR backplane

The 1770-XR uses a dedicated SRAM retention circuit that requires a minimum of approximately 3.0V at the battery terminals to hold memory contents. A depleted Li-SOCl2 cell can sit at or below this threshold while still appearing to read a nominal voltage on a multimeter — open-circuit voltage is not a reliable indicator of remaining capacity on thionyl chloride chemistry. The only safe approach is to replace the cell on a fixed maintenance schedule, not on measured voltage alone. Allen-Bradley documentation for this platform recommends replacement before the controller logs a low-battery fault.

Battery alarm not clearing after a confirmed good cell installation

The low-battery alarm on 1770-XR controllers does not reset automatically when a new cell is installed. The fault flag is latched in the controller's status file and must be cleared manually using RSLogix or your connected programming software. Navigate to the processor status file, locate the battery fault bit, and force it to zero with the controller in RUN mode. If the alarm returns within hours, check that the replacement cell is seated fully — a partially inserted cell creates intermittent contact that re-triggers the latch.