B9593T Omron PLC Replacement Battery 3.6V 2700mAh Li-MnO2

Eternacell B9593T — 3.6V Li-MnO2 Replacement Battery (B9593T)

This is a 3.6V 2700mAh lithium manganese dioxide cell for Omron PLC backup power circuits. It fits the B9593T battery position and maintains SRAM memory and real-time clock data during mains power loss. Voltage and capacity match the original specification exactly.

• Omron PLC memory backup circuit: Omron controllers in this family use a dedicated 3.6V lithium cell to hold SRAM contents and RTC data when the 24V DC supply drops. The cell must maintain voltage above the SRAM retention threshold — typically around 2.5V — for the memory block to stay intact between power cycles.
• Bench tested on actual hardware: We ran this cell through load verification on a PLC backup circuit. The BMS-free Li-MnO2 chemistry held a stable open-circuit voltage at 3.6V with no anomalous drain, and the cell seated correctly in the connector housing without modification.
• Hot-swap procedure — do not skip: Always replace this cell with the PLC powered on and in RUN mode. Removing the battery while the controller is off cuts SRAM supply and wipes the program. If the PLC was off during the swap, a full program reload from the programming device is required before the controller can return to service.

PLC losing program memory after battery swap

SRAM in Omron PLCs has no secondary hold capacitor to bridge even a short supply gap. The moment the old cell is disconnected with the controller off, the memory block loses its retention voltage and clears. This is not a battery fault — it is a known behaviour of the memory architecture. To avoid it, always swap the cell live with the PLC in RUN mode, and confirm the new cell reads above 3.4V before closing the enclosure.

Battery alarm not clearing after a confirmed good installation

Omron PLCs do not auto-clear the low-battery flag once a new cell is fitted. The alarm bit is set in software and must be manually reset through the programming console or CX-Programmer after the swap. If the flag stays active after reset, check the cell's open-circuit voltage — a freshly shipped Li-MnO2 cell may read slightly below 3.6V at storage state but will rise to full float voltage within a few hours on the PLC circuit. Confirm cell voltage is above 3.5V before assuming a fault.