Because the work is the volume of grass you remove, and that rises much faster than the height of the lawn suggests. Letting a lawn go an extra week can double what a pass costs.
Where the energy goes
Not mostly into cutting. A sharp blade slices a grass stem for very little. The energy goes into three other things.
Lift. The blade is a fan. It has to stand the grass up before the edge arrives, and moving that air is the largest continuous draw on the machine.
Transport. Every clipping has to be carried into the catcher, against gravity and friction, in an airstream. Long wet clippings are heavy and they stick.
Drag. Grass packed under the deck rubs on everything, and the motor pays for it until the deck is cleaned.
All three scale with how much material is passing through, not with how tall the lawn looks.
What makes it worse
A low cutting height, which takes more material per pass. Moisture, which makes clippings heavier and stickier. A dull blade, which tears rather than cuts and needs more force for a worse result. A full catcher, which restricts the airflow the deck depends on. And a clogged deck, which does the same thing permanently until it is scraped.
What recovers the runtime
Raise the height and take two passes rather than one. Mow when the grass is dry. Sharpen or replace the blade — it is the cheapest change on this list and the most overlooked. Empty the catcher before it packs, or remove it and mulch, which stops the airflow problem entirely.
And on a first cut of the season, accept that the machine is doing a different job and plan for two batteries or two sessions.
How this site handles it
The blade shelf here exists partly for this reason: a replacement blade is a runtime component on a cordless machine, not only a cutting one. Cordless mower pages print pack energy and state what the maker assumes; no page here publishes a runtime as if it were a property of the machine.
Wherever this page and the maker’s own documentation disagree, the documentation wins. Every cutting width, cutting height, stated area, pack capacity, flow rate, head, sound level and application rate on this page comes from the maker’s own published figures, with the unit as printed and the source named. None of it is measured here, and no figure is converted into another convention, because a converted number is a different number. And the division this page refuses to hide: a runtime is pack energy divided by a load, and the load is your grass. A published figure is a bench result obtained on short, dry grass at a middle setting, with no uncertainty attached and no obligation to state its conditions. This page prints capacity and platform voltage together, and reports any runtime as the manufacturer’s.
The questions that keep coming in
Is the mower faulty if it cuts out?
Usually not. A cordless machine that stops in heavy grass is generally its own protection acting on current or on temperature, and it restarts after a pause. A machine that stops on flat short grass and stays stopped is a different matter.
Does cutting higher really help that much?
It is the single most effective change. Less material per pass means less to cut, less to lift and less to move into the catcher, and all three costs fall together.
Last reviewed 26 September 2026