GreenWorks Optimow 4 Replacement Battery 20V 2000mAh

GreenWorks Optimow 4 / 5 / 7 — 20V Li-ion Replacement Battery (R0100999-00)

This 20V 2000mAh (40Wh) lithium-ion battery replaces the OEM pack in the GreenWorks Optimow 4, Optimow 5, and Optimow 7 robotic lawn mowers. It fits the docking station charge contacts and communicates with the mower's onboard BMS using the same handshake as the original pack. Swap it when your existing battery no longer holds charge or to keep a second pack cycling while the mower works.

• Optimow 4, 5, and 7 shared platform: All three models run the same 20V battery architecture, connector pinout, and BMS communication protocol. One battery works across the range without any modification to the docking station or mower firmware.
• Bench tested on actual hardware: We ran this pack through simulated blade-motor inrush events at the 20V nominal rail. The BMS held through normal load cycles and triggered cutoff correctly at the undervoltage threshold — no false trips under standard conditions.
• Seasonal storage before first spring use: If the mower sat docked through winter, check the pack voltage before reinstalling — self-discharge over several months can bring cells below the charger's acceptance threshold. Bring the battery indoors for 24 hours at room temperature before attempting a charge cycle.

Charger showing fault after the mower sat in the garage all winter

Li-ion packs left in storage self-discharge slowly over weeks. If the cell voltage drops below approximately 2.5V per cell, most chargers enter a fault or reject state rather than attempting a full charge — this is a protection circuit, not a defective charger or battery. The fix is a slow pre-charge recovery: some chargers will retry automatically if the pack is left connected for 15–30 minutes in a warm environment. If the charger continues to fault, the cells may have discharged too deeply for recovery and a replacement pack is the correct next step.

Mower cuts out mid-row then restarts on its own

This is thermal protection activating, not a battery fault. When blade motors work through thick or wet grass, current draw spikes and the pack temperature rises. The BMS cuts power to protect the cells, then resets once temperature drops back within range. Let the mower sit at the docking station for at least five minutes before restarting. If cutouts happen repeatedly on the same patch of lawn, the grass height may be too long for a single pass — lower the cutting area in the mower's schedule settings.