Flymo 18V 3000mAh Li-ion Compatible Battery FB18V2.5

My Flymo EasiTrim cut out halfway through the lawn and now it won't start again — is the battery dead or is it something else?

This is almost always thermal cutoff, not a dead battery — 18V Li-ion packs in cordless trimmers shut down hard when the cells overheat, especially if the line was buried in thick grass and the motor was labouring. Let the battery sit off the tool for 20 minutes in a cool spot, then try again. If it restarts fine but cuts out again after light use, the issue is cell imbalance — one cell is weaker and hitting its floor voltage before the others. Check the battery indicator: if it shows full charge but still cuts out under load, that cell imbalance diagnosis is likely correct and a replacement pack will fix it.

My Flymo trimmer runs but the cutting head feels like it's dragging — it spun fine on the old battery

Voltage sag under load is the most probable cause — if the replacement battery's cells aren't matched tightly, voltage drops the moment the motor pulls current, and the head loses torque without the battery appearing to be flat. This happens more often on 18V packs with mismatched cells than on the OEM units, which are cell-sorted at the factory. Put a multimeter on the battery terminals while the tool is running: resting voltage of 18–20V is normal, but if it drops below 15V the moment the head engages, the pack can't sustain the load. If that's what you see, the pack itself is the problem.

Flymo battery charged all night, charger light went green, but the trimmer dies after about two passes — what's wrong?

A green light confirms the charger finished a cycle, but it doesn't confirm the pack reached full capacity — Li-ion chargers terminate on voltage, not true capacity, so a degraded or deeply discharged pack can trick the charger into stopping early. Take the pack off the charger, wait 10 minutes, then put it back on: if the light immediately goes green again without any charge cycle running, the pack is either fully charged or the charger is failing to detect a fault. Charge it fully, then check the battery indicator — if it shows four bars but still dies under load, the capacity is there but one cell is collapsing; if it shows two bars or fewer after a full night, the pack isn't accepting charge properly and needs replacing.