About this replacement
Yamaha PRCX / QRCX / RCX Series — 3.6V Ni-MH Replacement Battery (KS4-M53G0-102)
This 3.6V, 4500mAh Ni-MH cell replaces the backup battery in Yamaha PRCX, QRCX, RCX40, and RCX142 industrial controllers. It maintains SRAM program memory and the real-time clock during power outages and scheduled maintenance. Cross-references OEM part numbers KS4-M53G0-101, KS4-M53G0-200, and N3000CR-3YA.
- PRCX / QRCX / RCX platform fit: These controllers share the same backup circuit voltage rail, connector footprint, and BMS handshake protocol — one cell covers the full group. Physically, the replacement matches OEM dimensions (76.65 × 50.40 × 26.16mm), so no bracket modification is needed.
- Bench tested on actual hardware: We ran this cell against the PRCX backup circuit under simulated mains loss. The BMS held SRAM at retention voltage without fault flags across repeated power-interruption cycles.
- Hot-swap is mandatory on this controller: Always replace this battery with the PLC powered on and in RUN mode. Removing the cell while the controller is off erases SRAM instantly — program data is gone and a full reload from the programming device is required. There is no grace period.
Why the PRCX loses program memory after a battery swap
The PRCX holds its ladder logic and parameter data in SRAM, which requires continuous voltage to retain contents. Unlike flash-based controllers, SRAM drops all data the moment supply voltage falls below the retention threshold — typically around 2.0V. If the old cell was removed while the controller was off, even a two-second gap clears memory completely. The only recovery path is reloading the program from a connected programming device or a saved backup file.
Battery alarm not clearing after a confirmed good installation
Fitting a new cell does not automatically clear the battery alarm on the PRCX — the controller latches the fault flag in software and holds it until a manual reset is performed in the programming environment. Navigate to the system diagnostics or status register in your programming software and clear the battery fault bit explicitly. A power cycle alone will not reset it. After clearing, confirm the alarm stays off through at least one full scan cycle before closing the enclosure.