AL-KO 18V 5000mAh Cordless Gardening Tool Replacement Battery

My AL-KO cordless pruner or hedge trimmer cuts fine then suddenly stops mid-job — is the battery dying or is something else cutting it out?

That sudden stop on 18V Li-ion garden tools is almost always thermal cutoff, not a dead cell — the pack gets warm during sustained blade load and the BMS shuts it down before anything is damaged. Let the battery sit off the tool for 10 minutes, then try again; if it runs normally after cooling, the issue is heat buildup under continuous use, not battery capacity. If it cuts out immediately on a cool battery, check the contact pins on the tool's battery slot for debris or corrosion — a dirty connection causes voltage sag that triggers the same protection circuit. Wipe the contacts with a dry cloth and test again before assuming the battery is at fault.

Put the new AL-KO battery on charge and the charger light just keeps blinking — never goes solid green, never says it's done.

A continuous blink that never resolves usually means the charger is detecting a cell voltage outside its acceptable intake range — this happens when a Li-ion pack has been stored flat and dropped below the charger's recovery threshold. Pull the battery off, wait 5 minutes, and reseat it firmly; sometimes the connection wasn't fully made and the charger is reading a false fault. If the blinking continues, check that the battery terminals are clean and that you're using an AL-KO-compatible 18V charger, since some third-party chargers in this voltage class use a handshake protocol the pack won't respond to. Measure the pack voltage at the terminals with a multimeter — a reading below 12V on an 18V Li-ion pack means it needs a slow-recovery charge cycle that most standard chargers won't attempt automatically.

AL-KO grass trimmer feels weaker than it did with the old battery — new battery, same tool, but the head spins slower and bogs down in thick grass.

A new 18V Li-ion pack that produces sluggish blade speed almost always points to a contact fit issue rather than a weak battery — if the battery isn't seating fully into the tool's receiver, resistance at the connection causes a voltage drop under load that looks exactly like a low-capacity pack. Press the battery in firmly until you hear or feel the latch click, then test again. If seating isn't the problem, check whether the tool's air vents are blocked with grass clippings; a thermally restricted motor draws more current, which pulls the battery voltage down and triggers the BMS to throttle output. Run the tool unloaded and listen — if the head spins freely at full speed with no grass contact, the battery is fine and the drag is mechanical.