About this replacement
Omron CPM2A / CQM1H / CJ1 — 3.6V Li-MnO2 Replacement Battery (CPM2A-BAT01)
This is a 3.6V 1000mAh lithium manganese dioxide cell that replaces the OEM CPM2A-BAT01 in Omron PLCs. It fits the CPM2A, CQM1H, CJ1, and NS7 series controllers, among others. Its sole job is to hold SRAM contents and keep the real-time clock running when mains power is absent.
- Multi-model fit across Omron compact PLC families: The CPM2A, CQM1H, CJ1, and NS7 all share the same 3.6V lithium cell format and pin-compatible connector. The backup circuit topology across these units draws from the same voltage rail, so one cell serves all of them without modification.
- Bench tested on actual hardware: We ran this cell on a CPM2A unit and confirmed the BMS float circuit accepted the cell immediately at rest voltage. SRAM retention held across simulated mains-loss events with no memory corruption detected.
- Hot-swap requirement on Omron PLCs: Always replace this battery with the PLC powered on and in RUN mode. Removing the cell while the controller is off drains the SRAM capacitor within seconds. If that happens, the program is gone and a full reload from a programming device is required.
PLC battery alarm not clearing after a confirmed good installation
On Omron CPM2A and CQM1H controllers, the battery alarm flag is latched in software — it does not clear automatically when a new cell is fitted. After installing the replacement cell, you must connect CX-Programmer (or the equivalent console), navigate to the PLC's error log, and manually reset the battery alarm flag. Until that step is done, the ERR/ALM indicator may stay lit even though the cell is good and reading the correct voltage.
Real-time clock showing wrong date and time after battery swap
If the PLC was powered off during the swap — even briefly — the RTC loses its count and defaults to a reset state. The new cell sustains the clock going forward but cannot recover the lost time reference. Connect CX-Programmer, go to PLC Clock under the Online menu, and set the current date and time manually. Confirm the write succeeded and verify the clock increments correctly before disconnecting.