26V Cub Cadet Lawnkeeper 1800 Compatible Battery 6Ah LiFePO4

My Lawnkeeper keeps returning to base early and showing a low battery error even after a full overnight charge — what's wrong?

This is almost always a cell capacity mismatch inside an aging Ni-MH pack — one or more cells have dropped below the threshold the mower's battery management system accepts, so it reads the whole pack as depleted even when voltage looks fine on a multimeter. A full charge on a degraded Ni-MH pack can still measure close to nominal voltage at rest but collapse under the load of the cutting motor within minutes of leaving the dock. The fix is a full pack replacement, not a recharge cycle. Before swapping, put a multimeter on the battery terminals mid-mow: if voltage sags below 10.5V under load, the pack is failing — replace it.

My Lawnkeeper stopped in the middle of the lawn and won't drive back to the dock — it's just sitting there with a flashing light.

Ni-MH packs that have sat through a winter without a maintenance charge often drop into a deep-discharge state the mower's onboard charger can't recover from — the pack voltage is too low for the charging circuit to even begin. This is different from a normal flat battery; the cells have self-discharged past the recovery floor, which is common in robotic mowers stored without the dock powered on. Try leaving the mower physically seated on the powered dock for 24 hours — some chargers will attempt a trickle recovery cycle. If the battery terminals read below 9V with no load, the pack won't recover and needs replacing.

I just put a new battery in my Lawnkeeper and now the cutting blade spins but the mower drives really slowly and barely moves — is that normal?

That symptom points to a voltage calibration mismatch — the mower's control board hasn't reset its battery state-of-charge model to match the new pack, so it's artificially limiting drive motor power to protect what it thinks is a weak battery. Power the unit fully off, remove it from the dock, leave it disconnected for two minutes, then reseat the battery and run a full charge cycle from empty before the first mow. If the slow drive persists after one complete charge-discharge cycle, check that the battery connector is fully seated — a half-connected Ni-MH pack will deliver enough voltage to spin the blade motor but starve the higher-current drive circuit.