McCulloch ROB 500 18V Replacement Battery 2500mAh Li-ion

McCulloch ROB 500 / ROB 600 / ROB 800 / ROB S400 — 18V Li-ion Replacement Battery

This 18V 2500mAh (45Wh) Li-ion battery fits the McCulloch ROB 500, ROB 600, ROB 800, and ROB S400 robotic lawn mowers. It replaces the original pack when capacity has faded or the battery no longer holds a charge. Voltage and connector match the OEM spec — no modifications needed.

• ROB 500 / 600 / 800 / S400 platform fit: These four models share the same 18V battery bay, connector pinout, and BMS handshake protocol. One battery covers all four mowers in the ROB range without any adapters or firmware changes.
• Bench tested on actual hardware: We ran this pack on a ROB 500 through full charge and discharge cycles. The BMS negotiated correctly, charge termination triggered at the expected voltage, and protection circuits responded normally to simulated load spikes from the blade motor.
• Seasonal storage before first spring use: Before the first mow of the season, bring the battery indoors overnight if temperatures are below 10°C. Cold Li-ion cells have higher internal resistance, and the blade motor's inrush current can trip the BMS on a cold pack before it even starts cutting.

BMS cutoff on thick-grass or wet-grass blade load

The ROB series blade motor draws significantly more current through dense or wet grass than on a dry, short lawn. If the instantaneous current exceeds the BMS trip threshold — typically caused by the motor stalling briefly against a clump — the pack shuts down as a protection measure. This is not a battery fault; it is the BMS doing its job. Returning the mower to the dock resets the BMS, and the pack recovers fully once the load drops below the cutoff threshold.

Charger showing a fault light after the mower sat unused all winter

Li-ion cells self-discharge slowly during storage. After several months in a cold garage, the pack voltage can drop below the charger's acceptance threshold — typically around 12–13V for an 18V pack — and the charger refuses to start a normal charge cycle. Some ROB chargers have a recovery or conditioning mode; holding the charge button for 5 seconds or leaving the pack on charge for 30 minutes at trickle voltage can bring the cells back above the acceptance floor. If the charger continues to fault, check the pack's resting voltage with a multimeter — a reading below 10V indicates the cells have discharged too deeply to recover.