Gardena 8654121 18V Replacement Battery 4000mAh

Gardena Automower 115H — 18V Li-ion Replacement Battery

This 18V 4000mAh (72Wh) Li-ion battery fits the Gardena Automower 115H robotic lawn mower across the 2019, 2020, and 2021 model years, along with the 8654121 platform. It slots into the battery bay and connects to the same BMS handshake the original pack uses. Voltage and connector match the cutting deck's motor controller exactly.

• Automower 115H 2019–2021 compatibility: These model years share the same 18V battery bay, connector pinout, and BMS communication protocol. The motor controller expects a specific handshake signal on wake-up — this pack delivers it, so the mower exits dock and begins its cutting schedule without error codes.
• Bench tested on actual hardware: We ran this pack through full charge and discharge cycles on the 115H platform. The BMS held voltage within spec under simulated blade-load surges, and the protection circuit responded correctly to over-current conditions without nuisance trips on normal grass.
• Seasonal storage tip for robotic mower packs: Before parking the mower for winter, charge the battery to around 50–60% — not full. A fully charged Li-ion pack stored for months accelerates cell degradation faster than a mid-state charge does.

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

The 115H blade motor draws significantly more current when cutting dense or wet grass compared to dry, short turf. If the inrush current spikes beyond the BMS threshold — typically caused by the mower hitting a thick patch at full speed — the pack cuts out as a protection measure. This is the BMS doing its job, not a battery fault. Letting the pack rest for five minutes allows the BMS to reset and the mower to resume.

Charger showing a fault light after winter storage

A battery that sat in an unheated garage all winter may have self-discharged below the charger's acceptance voltage threshold — typically around 10–12V for an 18V pack. Most Gardena chargers refuse to begin a charge cycle on a pack reading below that floor and show a fault or error LED. To recover it, try a different compatible charger that includes a trickle or recovery mode, or leave the pack in a warm room at 18–20°C for two hours before attempting charge again.