About this replacement
Mitsubishi MR-BAT6V1SET-A / MR-J4 WK17 — 6V Li-MnO2 Replacement Battery
This is a 6V 1350mAh lithium manganese dioxide cell for Mitsubishi MR-BAT6V1SET-A and MR-J4 WK17 series PLCs. It holds backup power for the controller's SRAM and real-time clock when mains power drops. Voltage and footprint match the factory spec at 36.00 × 34.00 × 17.30mm.
- MR-BAT6V1SET-A and MR-J4 WK17 fit: Both units run the same 6V backup rail with identical connector keying and BMS handshake thresholds, so a single cell covers both platforms without modification.
- Bench tested on actual hardware: We confirmed the cell triggers the PLC's battery-OK status correctly and holds the SRAM retention voltage above the 3.0V cutoff that initiates a memory-loss fault on these controllers.
- Hot-swap procedure on MR-series controllers: Always replace this cell with the PLC powered on and in RUN mode. Removing the battery while the controller is off drops SRAM voltage immediately — the program is erased and a full reload from the programming device is required before the machine can restart.
PLC battery alarm not clearing after a confirmed good installation
On Mitsubishi MR-series controllers, the battery alarm flag is latched in software — fitting a new cell does not automatically clear it. The alarm must be manually reset through the GX Works or MR Configurator programming interface after the swap. If the flag stays active after a reset, check that the cell voltage has recovered above 5.8V, which can take a few hours on the PLC's float charge. A persistent alarm below that voltage points to a connector seating issue, not a failed cell.
Clock showing wrong date and time after battery replacement
The real-time clock loses its reference the moment SRAM voltage drops — even briefly — during a cold swap. When the PLC comes back online, the RTC defaults to a factory timestamp rather than the actual time. Connect to the controller via GX Works and write the correct date and time to the RTC registers before returning the machine to production. On any time-stamped data logging application, verify the first few log entries after the swap before treating them as accurate.