Flymo 18V Cordless Grass Trimmer Replacement Battery 1500mAh

My Flymo Contour XT starts cutting then bogs down and the motor sounds like it's struggling through thick grass — is that the battery dying?

On Ni-MH packs at this capacity, voltage sag under load is the most likely cause — the cell group can't sustain current draw when the line head meets resistance, so the trimmer loses torque mid-cut even though the battery shows a charge. We saw this behaviour consistently on aged packs where one or two cells in the series string had drifted low, pulling the whole pack down under load. Before replacing, charge fully, let it rest 30 minutes, then test on light grass first — if it only bogs on dense growth, the pack is failing under load rather than sitting dead on the shelf.

Charged my Flymo grass trimmer overnight and it lasted about two cuts then stopped working completely — now the charger won't even light up when I plug the battery in

A Ni-MH pack that sits deeply discharged for an extended period can drop below the voltage threshold the charger uses to detect a valid battery — the charger sees it as a fault or an empty slot rather than a battery to recover. This is a known failure mode with 18V Ni-MH packs that have been stored flat, often after a season sitting in a shed. Some chargers have a recovery or reconditioning mode; check whether holding the battery in the charger for 20–30 minutes produces any change in the indicator light before assuming the pack is dead. If the charger light stays completely dark or flashes an error, measure the pack voltage with a multimeter — anything below roughly 12V on an 18V Ni-MH string means the cells have self-discharged into a range most standard chargers won't attempt to recover from.

Replaced the battery on my Flymo trimmer but the cutting line keeps stopping and starting even on a full charge — never did this with the old battery

This intermittent behaviour on a new Ni-MH pack is usually a contact problem rather than a cell problem — the terminal springs in the trimmer battery compartment compress over time and may not seat firmly against a new pack with slightly different cell casing dimensions. It can also happen if the pack hasn't gone through a full initial charge cycle, since fresh Ni-MH cells can deliver uneven voltage until they've been conditioned. Check that the battery clicks fully into the housing and that the metal contacts in the compartment aren't corroded or bent outward from the old pack. Run two full charge-and-discharge cycles before concluding there's a fault with the replacement pack.