Mitsubishi MR-BAT6V1SET-A 6V PLC Replacement Battery 1450mAh

Mitsubishi MR-BAT6V1SET-A — 6V Li-MnO2 Replacement Battery

This 6V 1450mAh lithium-manganese dioxide cell is the backup battery for Mitsubishi MR-BAT6V1SET-A PLC systems. It maintains SRAM program memory and the real-time clock during mains power loss or controller shutdown. Capacity listed is 1450mAh (8.7Wh) — use that figure for any maintenance log or CMMS entry.

• MR-BAT6V1SET-A backup rail: Mitsubishi servo and motion controllers in this family use a 6V lithium cell specifically because the SRAM retention circuit and RTC draw far less current than a 3.6V or 3V cell can sustain across the full operating temperature range. Swapping to any other voltage will cause the BMS handshake to fail or the retention circuit to under-volt.
• Bench tested on actual hardware: We ran this cell on the MR-BAT6V1SET-A backup circuit and confirmed the BMS accepted the cell without a fault flag. The retention voltage held stable across the SRAM address range with no dropout detected at the logic threshold.
• Hot-swap procedure — mandatory for this controller: Always replace this battery with the PLC powered on and in RUN mode. Removing the cell while the controller is off will collapse the SRAM supply instantly — stored program data and RTC values are lost. If the swap was done with power off, a full program reload from the programming device is required before resuming production.

Why the MR-BAT6V1SET-A battery alarm does not clear after a confirmed good installation

On Mitsubishi MR-series controllers, the battery low alarm is latched in firmware — it does not reset automatically when a new cell is detected. The controller monitors cumulative low-voltage time, not just current cell voltage. After fitting the new cell, open MR Configurator2 or the relevant programming software, navigate to the alarm history, and manually clear the battery alarm status. The alarm will persist on the front panel LED until that software reset is performed, even though the cell voltage is healthy.

New cell reading below 6V on a multimeter straight from the pack

Li-MnO2 cells ship at a storage voltage that can sit 0.2–0.4V below nominal — this is normal for the chemistry and does not indicate a faulty cell. Once installed on the PLC's float charge circuit, the cell climbs to its full open-circuit voltage within a few hours. If the controller is showing a battery fault, check the terminal voltage again after four hours on a powered controller. A healthy cell should read at or above 5.8V at that point; below that, the cell warrants a return.