Stiga Autoclip 720s 25.2V Replacement Battery 1126-9121-01

Stiga Autoclip 720s / 920s Series — 25.2V Li-ion Replacement Battery (1126-9121-01)

This is a 25.2V 13800mAh Li-ion replacement battery for the Stiga Autoclip robotic lawn mower range. It fits the Autoclip 720s, 920s, 125, and 127 models, all of which share the same battery bay, connector, and BMS communication protocol. Capacity is 13800mAh (347.76Wh), matching the original Stiga part 1126-9121-01.

• Autoclip 720s, 920s, 125, and 127 compatibility: These four models run the same 25.2V battery platform with an identical physical footprint, locking tab arrangement, and BMS handshake signal. One battery covers all four without any modification.
• Bench tested on actual hardware: We ran this pack through charge and discharge cycles on the Autoclip platform. The BMS communicated correctly with the mower's charge controller, accepted a full charge without fault codes, and delivered consistent voltage through the blade motor start surge.
• Seasonal storage tip: Before putting the mower away for winter, bring the battery indoors and store it at 50–70% charge. Li-ion cells left in an unheated garage below 5°C over several months will self-discharge toward the BMS lockout threshold — and the charger may refuse the pack come spring.

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

Stiga's charger checks pack voltage before it begins a charge cycle. If cells have discharged below roughly 18V over winter, the charger reads the pack as faulty and refuses to start. This is a BMS protection state, not a dead battery. Many packs can be recovered by using a compatible Li-ion charger with a recovery or boost mode to raise cell voltage above the acceptance threshold — typically 21V — before the main charge cycle begins.

Mower cuts out mid-row through thick or wet grass, then restarts after a few minutes

The blade motor draws a spike of current each time it hits dense or waterlogged grass. If that spike exceeds the BMS current threshold — more likely in a pack with aged cells — the BMS trips to protect the cells and the mower stops. The mower will restart once the BMS resets, usually after 3–5 minutes. A new pack with fresh cells handles the inrush better because internal resistance is lower, so the voltage sag during the spike stays within the BMS window.