Ferrex 800m2 20V Li-ion Replacement Battery 3400mAh

Ferrex 800m2 2021 — 20V Li-ion Replacement Battery

This is a 20V, 3400mAh (68Wh) Li-ion battery for the Ferrex 800m2 2021 cordless lawn mower. It slots into the same bay as the original pack and uses the same voltage rail the blade motor expects. Capacity is taken from the product specification — 3400mAh.

• Ferrex 800m2 2021 fitment: The 800m2 2021 runs a 20V motor circuit with a BMS handshake that checks cell voltage before releasing current to the blade drive. This pack matches that voltage rail and connector geometry, so the mower starts the handshake correctly on insertion.
• Bench tested on actual hardware: We cycled this pack under simulated blade-motor inrush loads. The BMS held at the correct cutoff threshold and recovered without fault codes across repeated load-and-rest cycles.
• First-season startup tip: Before the first mow of the season, bring the battery indoors overnight if temperatures are below 10°C. Cold Li-ion cells carry higher internal resistance, and the blade motor's inrush current can trip the BMS on a pack that hasn't reached ambient room temperature.

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

The 800m2 2021 blade motor draws significantly more current through dense or wet grass than on a clear, dry lawn. If that inrush spike exceeds the BMS protection threshold, the pack cuts power immediately to prevent cell damage. This is not a battery fault — it is the BMS doing its job. Slow down the mowing pass, let the blade reach full speed before entering the heavy section, and the draw stays within the BMS window.

Charger showing a fault light after the mower sat all winter

Li-ion cells self-discharge slowly over months of inactivity. If the pack voltage drops below the charger's acceptance threshold — typically around 12–14V on a 20V pack — the charger reads the pack as faulty and refuses to charge. Some chargers have a recovery or "wake-up" mode that applies a trickle current to bring the cells back into the acceptance window. If yours does not, check cell voltage with a multimeter; anything above 2.5V per cell is recoverable with a charger that supports soft-start charging.