About this replacement
Yamaha KR4-M4251-101 — 3.6V Ni-MH Replacement Battery
This 3.6V 1500mAh Ni-MH cell replaces the backup battery in the Yamaha KR4-M4251-101 PLC controller. It maintains SRAM program memory and the real-time clock when main power is removed. Without a working cell, the controller loses stored program data and clock settings on every power cycle.
- KR4-M4251-101 compatibility: This cell matches the voltage rail and physical footprint the KR4-M4251-101 uses for SRAM float charge. The Ni-MH chemistry holds a stable standby voltage that keeps memory retention active without active charging from the main power supply.
- Bench tested on actual hardware: We ran this cell at float charge and confirmed the BMS accepted it without a forced alarm state. Voltage settled within the SRAM retention window after a short stabilisation period from storage charge.
- Hot-swap procedure on the KR4-M4251-101: Always replace this battery with the PLC powered on and in RUN mode. Removing the cell while the controller is off will wipe SRAM instantly — program data cannot be recovered without reloading from a connected programming device.
PLC losing program memory after battery swap on the KR4-M4251-101
The KR4-M4251-101 uses the backup battery as the sole power source for SRAM when main supply is off. If the cell is removed — even briefly — while the controller is not powered, SRAM collapses and the entire program is lost. There is no capacitor buffer on this unit to cover a swap. Reconnect the programming device, reload the last saved program, and verify the real-time clock settings before returning the controller to service.
Battery alarm not clearing after fitting a new cell
The KR4-M4251-101 does not auto-clear a low-battery alarm once a new cell is installed. The fault flag is set in software and must be manually reset through the programming interface — the controller will continue to display the alarm regardless of actual cell voltage. Open the programming software, navigate to the fault log or battery status register, and clear the flag explicitly. Confirm the cell voltage is reading above 3.4V before closing the session.