AL-KO GS 7.2 Li Multicutter Replacement Battery 7.4V 2000mAh

My AL-KO GS 7.2 Li multicutter starts cutting then slows down and feels weak halfway through a shrub — is the new battery the problem?

At 7.4V with a small Li-ion cell like this, the most likely cause is voltage sag under load — the blade motor draws a spike of current when it hits thick stems, and a battery that wasn't fully conditioned before first use can't hold its voltage through that. Run two or three full charge-discharge cycles before deciding the battery is faulty. Then check the resting voltage with a multimeter after a full charge — it should read between 8.3V and 8.4V; anything below 8.0V off the charger points to a cell not reaching capacity.

The AL-KO charger just sits there with no light after I plugged in the new replacement battery — nothing's happening at all.

This usually means the battery voltage has dropped low enough that the charger can't recognise it as a valid pack — a common outcome when a Li-ion battery has been stored discharged for a long time before reaching you. Some AL-KO chargers have a recovery threshold and won't initiate a charge cycle below roughly 5–6V per cell. Try leaving the battery connected for 20–30 minutes with no load; some chargers will trickle-feed a deeply discharged pack back into the normal charge window before the indicator activates. If nothing happens after that, measure the pack voltage at the terminals — below 5V across both cells means the pack is in deep discharge and the charger may need a compatible recovery mode to revive it.

New battery charged fine but the AL-KO grass shear cuts for a few seconds then stops and won't restart until it cools down — what's going on?

That stop-and-restart pattern is thermal cutoff triggering, not a dead battery. The protection circuit inside the pack is shutting down current when cell temperature exceeds its safety threshold — on a compact 7.4V Li-ion this can happen quickly if the blade is snagged, partially blocked, or if the tool is being used continuously without short pauses on dense growth. Check that the blade isn't binding or gunked up with plant debris, because a stalled or dragging blade pulls much higher current than a free-spinning one. If the tool trips immediately even on light cutting, the protection board may be oversensitive — measure cell voltage after a trip; if it reads above 7.0V the cells are fine and the fault is thermal, not capacity.