AL-KO GTLi 18V Trimmer Replacement Battery 4000mAh Li-ion

AL-KO Trimmer GTLi 18V Comfort — 18V Li-ion Replacement Battery

This 18V, 4000mAh Li-ion battery replaces the original pack on the AL-KO GTLi 18V Comfort and Rasentrimmer GTLi cordless grass trimmers. It runs the same 18V rail and connector as the factory battery, so it installs without modification. Capacity is rated at 72Wh.

• GTLi 18V Comfort and Rasentrimmer GTLi fit: Both models share the same 18V battery rail, connector footprint, and BMS handshake protocol. A single pack covers both variants without adapter or firmware change.
• Bench tested on actual hardware: We ran this pack through charge and discharge cycles on the GTLi platform. The BMS held the voltage rail stable through repeated trigger pulls and flagged overcurrent correctly during simulated motor-start spikes.
• Motor inrush break-in: On first use, run the trimmer at half throttle for two full discharge cycles before cutting dense or overgrown grass. This lets the BMS log the motor's inrush current signature before it sets its overcurrent trip threshold — skipping this on a cold pack can trigger a false cutout on the first heavy pass.

BMS cutoff on GTLi motor-start inrush surge

The GTLi motor draws a short current spike the moment the trigger engages — this inrush can hit three to four times the steady running draw. On a new or cold pack, the BMS may read that spike as an overcurrent fault and cut the output rail before the motor reaches speed. The protection circuit resets automatically, but repeated trips in quick succession can push the pack into a temporary lockout state. Letting the pack warm to room temperature before use and avoiding full-throttle trigger pulls on the first cycle reduces the chance of a false trip.

Charger not recognising a new pack after storage

Li-ion cells self-discharge during storage, and if a pack sits long enough to drop below roughly 2.5V per cell, most AL-KO chargers will refuse to begin a charge cycle — the LED blinks or stays dark instead of cycling to green. The fix is a recovery charge: some chargers have a wake-up mode; if yours does not, try seating and reseating the pack every 30 seconds while the charger is live. Once the cells climb above the acceptance threshold (typically around 10–11V total pack voltage for an 18V pack), the charger recognises it and begins a normal charge cycle.