About this replacement
Okuma MB4000 / LB3000 EX II-MY — 9.6V Ni-MH Replacement Battery (8HR-4/3FAUPC)
This 9.6V, 3600mAh Ni-MH cell supplies backup power to the Okuma CNC controller's SRAM and real-time clock when mains power is lost or the machine is shut down. It fits the MB4000, MB4000a, and Lathe LB3000 EX II-MY control systems. Without a functional battery, the controller loses its stored programs, tool offsets, and clock data.
- MB4000, MB4000a, and LB3000 EX II-MY compatibility: These controllers share the same 9.6V battery rail, connector footprint, and BMS handshake — all three accept the 8HR-4/3FAUPC cell format. Part numbers E5503-07E-001 and 5PBH-96360 cross-reference to the same cell.
- Bench tested on actual hardware: We ran this cell through full charge cycles on a CNC controller test rig and confirmed the BMS accepted the charge handshake without fault. SRAM retention voltage held above threshold throughout the discharge curve.
- Hot-swap is mandatory on this controller: Never remove this battery while the Okuma controller is powered off. Always swap the cell with the PLC powered and in RUN mode. If the controller was off during the swap, SRAM is lost and a full program reload from your programming device is required.
Why the Okuma MB4000 loses program memory after a battery swap
The MB4000 controller uses SRAM for program and parameter storage. SRAM is volatile — it requires continuous voltage to retain data. The moment battery voltage drops below the SRAM retention threshold (typically around 3V at the cell level), all stored data is cleared. A cold swap with the machine off guarantees that drop occurs. The only recovery path is reloading the full program and re-entering tool offsets from a backup file on your programming device.
Battery alarm not clearing after a confirmed good installation
A fresh cell won't automatically cancel the low-battery alarm on the Okuma controller. The alarm flag is written to a register in the control software and must be cleared manually — fitting a new battery does not reset it. Navigate to the maintenance or diagnostic screen in the controller software and reset the battery alarm flag directly. If the alarm returns within a short period, check that the cell voltage has risen from storage level (typically around 8.5–9V) to full charge — the float charge circuit on the controller will bring it to rated voltage within a few hours of powered operation.