About this replacement
Mitsubishi MelServo MR-J3 Series — 3.6V Li-MnO2 Replacement Battery (MR-J3BAT)
This is a 3.6V, 2000mAh lithium-manganese dioxide cell that replaces the OEM MR-J3BAT backup battery in Mitsubishi MelServo MR-J3 servo drives. It holds SRAM retention voltage to protect stored servo parameters and keeps the real-time clock running during a mains power outage. Fits MelServo MR-J3, MR-J3-A, MR-J3-A4, MR-J3-B, and additional drives in the MR-J3 family.
- MR-J3 series compatibility: All MR-J3 variants use the same 3.6V backup circuit and BAT connector footprint. The BMS handshake is identical across MR-J3, MR-J3-A, MR-J3-A4, and MR-J3-B, so one cell covers the full range without configuration changes.
- Bench tested on actual hardware: We ran this cell against the MR-J3 backup circuit and confirmed stable float charge acceptance and correct low-voltage alarm threshold behaviour. The drive's battery monitoring circuit flagged depletion at the expected voltage and cleared the alarm cleanly after swap.
- Hot-swap procedure — MR-J3 specific: Always replace this battery with the servo drive powered on and in RUN mode. The MR-J3 SRAM has no capacitor hold-up circuit — removing the cell while the drive is de-energised wipes stored parameters instantly, requiring a full program reload from a connected programming device.
MR-J3 battery alarm not clearing after a confirmed good installation
Fitting a new MR-J3BAT cell does not automatically reset the low-battery alarm in the drive. The MR-J3 latches this fault in its error log and holds the alarm output until it is manually cleared through MR Configurator or the servo amplifier's front panel. A new cell at storage voltage — typically around 3.0V to 3.2V — also reads below the drive's "battery OK" threshold until the float charge tops it up. Clear the alarm in software after installation, then confirm the cell voltage has risen above 3.5V before closing the cabinet.
MR-J3 real-time clock showing wrong date and time after battery replacement
If the drive was powered off during the battery swap, the RTC loses its reference and resets to a default timestamp — commonly 2000-01-01 00:00. The MR-J3 does not sync the clock automatically on power-up. Reconnect MR Configurator, navigate to the clock settings under the drive parameters, and set the correct date and time manually. Confirm the new value is retained through a full power cycle before returning the axis to service.