About this replacement
Okuma MX50 — 3.6V Li-SOCl2 Replacement Battery (A911-2817-01-010)
This is a 3.6V lithium thionyl chloride cell rated at 3500mAh, built to maintain SRAM program memory and real-time clock function in the Okuma MX50 CNC controller. It replaces OEM part numbers A911-2817-01-010, A911-2817, A9112817, and E5503-490-012. When this cell depletes, the MX50 loses its stored program data and operational parameters on the next power cycle.
- MX50 and MX-50 controller fit: Both designations reference the same Okuma controller hardware. The battery slot, connector, and voltage rail are identical across these variants — this cell fits without modification.
- Bench tested on actual hardware: We confirmed open-circuit voltage, verified the cell holds above 3.5V under light SRAM retention load, and checked that the BMS does not interrupt the backup current path during insertion.
- Hot-swap procedure for the MX50: Always replace this cell with the controller powered on and in RUN mode. Removing the battery while the MX50 is powered off will erase SRAM contents immediately. If a cold swap has already occurred, a full program reload from the programming device is required before the machine can run.
Why the MX50 battery alarm stays active after a new cell is installed
The MX50 does not automatically clear the battery alarm once a fresh cell is detected. The alarm flag is set in software and must be manually reset through the Okuma programming interface or ladder logic after the swap. Skipping this step leaves the alarm active even with a healthy cell seated correctly. Navigate to the battery alarm reset parameter in the controller's diagnostic menu and confirm the flag is cleared before resuming production.
New cell reading below 3.6V on the MX50 battery monitor screen
Li-SOCl2 cells ship at a storage voltage that can read as low as 3.4V out of the packaging — this is normal for this chemistry. The cell is not faulty. Once seated in the MX50 with the controller powered on, the float charge circuit brings the cell to its rated voltage within a few hours. If the monitor still reads below 3.5V after 24 hours of normal controller operation, seat the cell again to confirm contact and re-check.