18V AL-KO Comfort GT 1825 String Trimmer Compatible Battery

My AL-KO GT 1825 trimmer starts fine then bogs down and loses power halfway through edging — is that the battery?

Most likely yes — this is voltage sag under load, which happens when a Li-ion pack can't sustain current draw through dense grass or thick stems. The trimmer's motor pulls hardest during the cut, and an underperforming cell drops voltage faster than the tool's protection circuit expects. Before assuming the battery is dead, fully charge it, then check the terminal voltage with a multimeter immediately after it bogs — a healthy 18V pack should read above 16V under light load. If you're seeing below 15V during use, the pack is failing to hold voltage and needs replacing.

The AL-KO battery feels warm after charging but the trimmer still cuts out after a few passes — why?

Warmth after charging is normal, but cutting out immediately under working load usually means one or more cells inside the pack have lost capacity and the battery management system is tripping the overcurrent or undervoltage protection to prevent damage. This is more common in packs that sat unused through winter or went through shallow charge cycles repeatedly without a full charge. Let the battery cool completely, charge it to full, and then test it on a light section of lawn — if it still cuts out within the first few passes, the pack capacity has dropped below what the motor needs to run cleanly. At 2000mAh this pack has limited headroom, so even partial cell degradation shows up quickly in a high-draw trimmer.

New replacement battery for the GT 1825 is fully charged but the trimmer runs noticeably slower than it used to — what's wrong?

A new Li-ion pack sometimes needs two or three full charge and discharge cycles before the cells settle and deliver their rated output consistently. If the trimmer is running slow from the very first use, check that the battery is fully seated and the terminals are making clean contact — debris or corrosion on the trimmer's battery contacts can increase resistance and drop the voltage reaching the motor. Clean the contacts on both the tool and the battery with a dry cloth, reseat the pack firmly, and run a full charge cycle before testing again. If it's still sluggish after two full cycles, the pack itself may have a cell balance issue — check that the charger shows a normal green completion light rather than a fault blink.