Why Does My Battery Lawn Mower Leave Uncut Strips? Six Causes and the Fix for Each

The short answer

A battery mower leaves uncut strips for one of six reasons: the blade is dull, damaged or fitted wrong; the blade is turning too slowly for the grass; the mower is being walked too fast or overlapped too little; the deck is packed with wet clippings; the wheels are pressing the grass flat before the blade reaches it; or the deck is sitting unevenly. Battery mowers are more prone to strips than gas mowers because their blades turn more slowly, and because eco modes and tired packs slow them further. Each cause leaves a different pattern, and the pattern tells you where to look.

Read the pattern first

Strips in the same place on every pass, usually a narrow line at one edge of the cut, point to the blade or the deck. A strip down the center of a twin-blade mower points to one blade. Strips that appear only in thick or wet grass and vanish on the thin lawn point to blade speed, walking pace or a clogged deck. Strips that line up with the wheel tracks point to flattened grass. Random tufts everywhere point to a dull blade or a blade turning too slowly to lift the grass before cutting it.

Cause one: a dull, bent or wrong blade

A sharp blade cuts grass; a dull one tears and pushes it over, and the pushed-over blades stand up again after the mower has passed. Battery mowers hide a dull blade longer than gas mowers because the slower blade makes a less obvious ragged cut, so the strips are often the first sign. Tip the mower back on its wheels, with the pack removed, and run a finger along the cutting edges. If they are rounded, nicked or rolled over, sharpen or replace. While the blade is off, check it is fitted with the wings or lift tabs pointing up into the deck; a blade fitted upside down cuts almost nothing and the strips are everywhere. On a twin-blade deck, measure both blades. If one has been sharpened shorter or is bent, the two cutting circles no longer overlap and a strip is left down the middle.

Cause two: blade speed

A mower blade does two jobs: the lift tabs at the rear create suction that stands the grass up, and the edge cuts it. Both depend on speed. A gas mower turns its blade at a fixed high speed; a battery mower turns it as fast as the motor and the pack allow, and several things slow it. Eco mode is the first; it drops blade speed to stretch runtime and should be switched off whenever the grass is thick, damp or more than a third taller than the cutting height. A pack near empty is the second; many mowers reduce power as the pack sags, and a cold pack sags sooner. An old pack with high internal resistance is the third, and it shows as a mower that cut fine two summers ago and leaves strips now on the same lawn. Mow the thick areas first on a fresh, warm pack in full-power mode and see if the strips vanish.

Cause three: walking too fast, overlapping too little

A blade turning at a given speed can only cut so many blades of grass per second. Walk faster than that and the mower passes over grass it has not cut. Self-propelled battery mowers with a top speed set for a gas mower are the usual culprits. Slow down in thick grass, and overlap each pass by a third of the deck width rather than lining the wheel up with the last cut edge. The outer inch of a battery mower deck often cuts poorly because the blade tip is the slowest point of lift, and that is the strip that appears when passes are butted edge to edge.

Cause four: a clogged deck

Wet clippings pack into the underside of the deck and under the mulching plug, and they do two things: they fill the space the blade needs to lift grass into, and they add drag that slows the blade. Strips appear, and the mower sounds labored and smells of hot grass. Remove the pack, tip the mower and scrape the deck clean after every wet mow. Mow when the grass is dry, raise the cutting height a notch for the first pass on long grass and lower it for a second, and consider bagging or side discharge instead of mulching when the lawn is damp.

Cause five: grass flattened by the wheels

The front wheels run over the grass before the blade reaches it, and in tall or damp grass they press it flat. Some of that grass stands up again after the mower has passed and shows as uncut lines along the wheel tracks. The fix is to mow in a different direction each time so flattened grass is cut on the next pass, to raise the cutting height in tall grass, and to mow more often so the grass is never tall enough to lie down. Mowing when the dew has dried helps because dry grass springs back under the wheels.

Cause six: an uneven deck

A single-blade deck that sits lower on one side cuts a sloped swath and leaves a strip on the high side. Check that all four wheels are set to the same height; on mowers with individual wheel adjusters one lever is often knocked a notch. Check for a bent axle or a wheel with a worn or missing bushing. Put the mower on a flat floor and measure from the floor to the blade tip at both sides; they should match within a few millimeters.

A checklist in order

Switch off eco mode and fit a full, warm pack. Mow slower and overlap by a third. If strips remain, clean the deck and check the blade for edge, damage and orientation. If strips remain and the mower is twin-blade, measure both blades. If strips remain, check wheel heights. Sharpen or replace the blade twice a season and after any strike, and the mower that leaves strips usually stops.