Kawasaki MD500N PLC Compatible Battery 3.6V 3500mAh

Kawasaki MD500N — 3.6V Li-SOCl2 Replacement Battery (50750-1018)

This is a 3.6V, 3500mAh lithium-thionyl chloride cell that replaces OEM part 50750-1018 in the Kawasaki MD500N helicopter. It powers the onboard PLC's SRAM retention circuit, keeping the flight control program memory intact when main power is off. Li-SOCl2 chemistry is specified here because of its flat discharge curve and low self-discharge over long maintenance intervals.

• MD500N PLC retention circuit: The MD500N's programmable logic controller holds flight-critical program data in volatile SRAM. This cell supplies the standby voltage that keeps that memory alive between power cycles. Voltage, connector geometry, and cell dimensions match the 50750-1018 footprint directly.
• Bench tested on actual hardware: We confirmed open-circuit voltage at 3.6V before dispatch and verified the cell holds above the 3.0V SRAM retention threshold under a simulated low-drain standby load. No anomalous self-discharge was observed during the test window.
• Hot-swap procedure for MD500N: Always replace this cell with the PLC powered on and in RUN mode. Removing the battery while the controller is de-energised will cause SRAM to lose program data immediately. If the PLC was off during the swap, a full program reload from the ground support programming device is required before returning the aircraft to service.

PLC losing program memory after battery swap on the MD500N

Li-SOCl2 cells power SRAM directly — there is no secondary capacitor buffer on most PLC retention circuits in this aircraft. The moment the old cell is disconnected and the new one is not yet seated, SRAM voltage collapses and all stored program data is lost. This is not a fault with the replacement cell. The only prevention is a live hot-swap: old cell out, new cell in, with the controller powered and in RUN mode throughout. If memory was lost, reload the program from the authorised ground station before any system test.

Battery alarm not clearing after fitting a confirmed good cell

The MD500N PLC does not auto-clear a battery fault flag when a new cell is installed — the alarm latches in firmware until it is manually acknowledged. After seating the 50750-1018 replacement, connect the programming device and clear the battery alarm bit through the diagnostic or status screen in the controller software. Confirm the cell is reading at or above 3.5V in the live diagnostics before clearing. If the alarm returns within minutes, check the cell contact pins for oxidation or misalignment.