Okuma MB500 PLC Replacement Battery 3V 5000mAh E5503-702-003

Okuma MB500 — 3V Li-MnO2 Replacement Battery (E5503-702-003)

This 3V lithium manganese dioxide cell replaces the OEM backup battery in the Okuma MB500 CNC machine control system. It fits controllers running OSP-P200 and P20 software platforms and carries a 5000mAh (15Wh) capacity. The cell powers SRAM retention, keeping machining programs, offsets, and parameters safe during any power interruption.

• OSP-P200 and P20 platform fit: Both control variants use the same 3V CR-format cell with identical footprint, connector, and BMS handshake requirements. One part number — E5503-702-003 — covers both platforms because the SRAM retention circuit draws from the same voltage rail.
• Bench tested on actual hardware: We ran this cell under continuous low-current SRAM load and confirmed the BMS holds stable output across the full rated capacity range. Voltage stayed flat through discharge, which is consistent with Li-MnO2 chemistry under standby draw.
• Hot-swap procedure on the MB500: Always replace this cell with the Okuma controller powered on and in RUN mode. Removing the battery while the machine is shut down will wipe SRAM instantly — programs, tool offsets, and system parameters will be gone. If the PLC was off during the swap, a full program reload from the programming terminal is required before the machine can run.

MB500 losing program memory after battery swap

SRAM on the Okuma OSP control has no capacitor buffer — the moment battery voltage drops below the retention threshold, stored data is gone. This happens most often when a technician swaps the cell with the machine powered down. Even a five-second gap is enough to clear memory at the SRAM chip level. The only recovery path at that point is reloading programs and parameters from an external backup via the programming terminal.

Battery alarm not clearing after a confirmed good cell is installed

The Okuma OSP control does not auto-clear the battery alarm when a new cell is detected. The fault flag is written to a non-volatile register and must be reset manually inside the maintenance or diagnostic screen of the OSP software. Navigate to the alarm reset function in the OSP interface, confirm the new cell is seated and showing voltage, then clear the flag. If the alarm returns within hours, check enclosure temperature — cells in warm cabinets above 40°C self-discharge at roughly double the rated rate, which can trigger the low-voltage alarm prematurely.