36V Kärcher Cordless Lawn Mower Replacement Battery 5000mAh

Mower cuts fine then suddenly stops mid-lawn and won't restart for a few minutes — what's happening?

That's thermal cutoff triggering in the battery pack, not a fault with the cells themselves. The LMO 36-40 pulls hard through thick or damp grass, and a 36V Li-ion pack will shut itself down before it overheats to protect the cells. Let the battery sit off the mower for around 10 minutes and check whether the tool restarts normally — if it does, thermal cutoff was the cause. To reduce how often it trips, raise the cutting height one notch and avoid mowing wet grass.

New battery fits in the mower but the blade won't spin — no lights, no error, just nothing happens?

A brand-new Li-ion pack sometimes ships in a deep sleep state after sitting in storage, and the mower's trigger circuit won't wake it the way a charger will. Seat the battery in its Kärcher 36V charger first and confirm the charge indicator shows activity — even a briefly flashing light means the pack is recovering. If the charger shows no response at all, press the battery's charge-level button and check whether any LEDs light; zero LEDs on a new pack points to a sleep-state that needs a slow-charge wake cycle. Leave it on charge for a full cycle before fitting it back in the mower.

Battery shows full charge but the mower bogs down and loses power halfway through a normal-sized lawn?

Voltage sag under load is the likely cause — the pack reads full at rest but can't hold voltage once the blade motor demands current through dense grass. This is more pronounced if the previous battery was heavily cycled and you're comparing performance, or if the new pack hasn't completed its first two or three full charge-discharge cycles, which is when Li-ion cells settle into their rated capacity. Check the resting voltage with a multimeter after a full charge; a healthy 36V Li-ion pack should read between 40V and 42V off the charger. If the reading is normal but sag persists after three cycles, the issue is more likely a partially blocked deck or a dull blade increasing motor load — clean the underside and check blade condition before assuming the battery is the problem.