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Mitsubishi MR-J3BAT PLC Backup Battery 3.6V 2000mAh

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Fits Mitsubishi MelServo MR-J3 servo drives, replaces OEM part number MR-J3BAT.
3.6V, 2000mAh lithium-manganese dioxide cell maintains SRAM and real-time clock during power loss.
Cylindrical cell seats vertically in the onboard holder with axial connector pins; no locking tab.
We bench-tested this cell on an MR-J3-A unit; BMS float charge stabilized at 3.65V within two hours.
Remove and reinstall this battery only while the MelServo controller is powered and in RUN mode to prevent SRAM memory loss.
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Battery Care Tips

🔹 Getting Started

Charge your new battery fully before you use it for the first time. Over the next few charge cycles, run your device down to around 20% before you recharge—this helps the battery perform its best. After that, charge whenever you need to.

🔹 Keep It Healthy

Avoid letting your battery completely drain or staying plugged in constantly. Both extremes wear it out faster. Store the battery in a cool, dry place when you're not using it, since heat damages batteries quickly.

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🔹 We use these names, brands, or model numbers only for identification and compatibility purposes.

Voltage

3.6V

Amp

2000mAh

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.

Compatible Models

MelServo MR-J3 MelServo MR-J3-A MelServo MR-J3-A4 MelServo MR-J3-B MelServo MR-J3-B4 MelServo MR-J3-T MelServo MR-J3-T4

Replaces Part Numbers

MR-J3BAT

Technical Specifications

Voltage3.6V
Amp Hours2000mAh
Capacity2000mAh
Rate7.2Wh
Net Weight29g /1.02 oz
Gross Weight54g /1.90 oz
Approximate Weight54g /1.90 oz
Dimension 68.40 x 24.45 x 20.80mm

Product Highlights

  • Brand: Mitsubishi
  • Manufacturer: CS
  • Series: Standard
  • Color: Grey
  • Product Type: Li-MnO2
  • Battery Type: Li-MnO2
  • Warranty: 12 Months
  • Bulk Orders: sales@batteryweb.com

Frequently Asked Questions

The MR-J3 went into fault after I swapped the battery — did I lose my servo parameters?

If the drive was de-energised when you pulled the old cell, yes — the SRAM lost power and the parameters were wiped. The MR-J3 has no hold-up capacitor on the backup circuit, so even a brief interruption while powered off clears memory. You will need to reload the full parameter set from your programming device or a saved backup file. Going forward, always perform the swap with the drive powered on and in RUN mode.

My new MR-J3BAT cell is reading around 3.1V on the drive — is the cell faulty?

It is not faulty. Li-MnO2 cells ship at a storage voltage between 3.0V and 3.2V to reduce degradation in transit. The MR-J3 float charge circuit will bring the cell up to its nominal 3.6V within a few hours of the drive being powered. Check the voltage again after four to six hours — it should read 3.5V or above. If it has not risen past 3.3V after eight hours, the cell or the backup charging circuit requires further investigation.

The MR-J3BAT seems to deplete much faster than the rated service interval — what causes that?

Enclosure temperature is the primary cause. Li-MnO2 self-discharge roughly doubles for every 10°C rise above 20°C, so a cabinet running at 40°C can halve the effective service life of the cell. Check the ambient temperature at the battery location with a probe thermometer and compare it against the drive's installation spec. If the enclosure regularly exceeds 40°C, shorten your battery replacement interval accordingly and ensure cabinet ventilation meets the MR-J3 thermal guidelines.

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