How to Choose a Cordless Lawn Mower: Deck Width, Voltage, Drive Type and Deck Material by Yard Size

The short answer

Pick the deck width by your lawn size, the voltage and amp-hour rating by how thick and long the grass gets, and self-propelled drive by slope and your own stamina. For a flat lawn under a quarter acre, a 40V push mower with a 16 or 17 inch deck and a 5 or 6 Ah pack is enough. For a quarter to half acre, step up to a 20 or 21 inch deck, a 56V to 80V platform and self-propelled drive, with two packs on hand. Beyond half an acre a cordless mower still works, but you will be swapping packs, and a second set is part of the price. Those three decisions cover most of it; the rest of this article explains each one and the smaller choices that follow from it.

Deck width and yard size

Cordless mowers run from about 14 inches to 21 inches across the deck. A 14 or 16 inch deck suits a small city lot up to about 5,000 square feet, fits through a 30 inch gate and stores in a tight corner. A 17 to 19 inch deck is the middle ground for lawns up to about a quarter acre. A 20 or 21 inch deck covers a quarter to half acre in reasonable time and matches the width of a gas push mower, which is what most people are used to. Every extra inch of deck is less walking, but it is also a heavier mower, a bigger motor and a faster drain on the pack. A rough rule: a 21 inch deck mows about 40 percent more lawn per pass than a 15 inch one, and draws about that much more current doing it, so the pack has to grow with the deck.

Voltage and amp-hours

Voltage sets how much power the motor can deliver; amp-hours set how long the pack lasts. Platforms run from 40V at the low end through 56V, 60V and 80V at the top. In practice a 40V mower handles a well-kept lawn fine, a 56V or 60V mower handles thick spring growth and damp grass without bogging, and 80V is for tall, dense grass and the widest decks. Runtime is the product of the two numbers. A 40V 5 Ah pack holds about 180 watt-hours and mows roughly a fifth of an acre of ordinary grass; a 56V 7.5 Ah pack holds about 400 watt-hours and covers roughly half an acre. Those figures fall by a third or more in thick, wet grass or with the mulch plug in, so size the pack to the worst week of the season, not the average. Two mid-size packs beat one huge one, because one can charge while the other runs.

Push or self-propelled

A push mower is lighter, cheaper and has fewer parts to fail, and on a flat lawn under a quarter acre it is the better buy. Self-propelled drive adds 10 to 15 pounds, a drive motor that draws from the same pack, and a price premium, but on a slope, a lawn with long rows, or for anyone who finds pushing 60 pounds tiring, it is worth every bit of that. Rear-wheel drive pulls better on hills and when the bag is full; front-wheel drive is cheaper and pivots more easily around beds. Look for a variable speed control rather than a single fixed pace, because a drive that walks faster than the blade can cut leaves strips of uncut grass.

Brushless or brushed

A brushless motor runs cooler, lasts longer, uses less of the pack for the same cut and adjusts its speed to the load, so it speeds up in thick grass and eases off in thin. Nearly every mower above the bargain tier is brushless now, and it is worth insisting on. A brushed motor is found on the cheapest 14 and 16 inch mowers and is fine for a tiny lawn cut weekly, but it wears its brushes, runs hotter and drains the pack faster.

Steel or poly deck

Most cordless mowers use a molded polymer deck. It is light, never rusts, and is shaped for airflow so it mulches and bags well. A steel deck is heavier, dents rather than cracks when it meets a root, and takes a bigger blade and motor; it is the norm on 21 inch self-propelled machines built to replace a gas mower. For a small lawn with no rocks, poly is fine. For a rough lawn, a steel deck shrugs off the knocks. Either way check the cutting height range: about 1.25 inches at the low end and 3.5 to 4 inches at the top suits most grasses, and a single lever that lifts all four wheels at once is far easier to live with than four separate adjusters.

Mulch, bag or side discharge

Three-in-one mowers do all three; two-in-one mowers mulch and bag. Mulching returns clippings as fertilizer and is the default for weekly mowing, but it loads the motor hardest. Bagging keeps the lawn tidy, collects leaves in fall and lets you mow long grass in one pass, at the cost of emptying a 1.5 to 2 bushel bag every few rows. Side discharge is the easiest on the pack and the best for grass that has gotten away from you, and it is the option cheap mowers leave out. Buy the three-in-one if the lawn ever gets long.

Battery platform, weight and storage

The pack is the expensive part, and it also decides your next five tool purchases. If you already own a 40V blower or a 56V trimmer, buy the mower on that platform and skip the kit price. If you are starting fresh, pick a platform with a blower, trimmer and hedge trimmer you would actually want, and check that a larger pack is sold for the mower. Weigh the mower too: a 16 inch push model is about 40 to 50 pounds, a 21 inch self-propelled steel deck 70 to 90 pounds with the pack in. Most cordless mowers fold the handle and stand upright on their rear wheels, which cuts the storage footprint to about a third of a gas mower; confirm the handle folds without tools and that the mower can stand vertically with the pack removed.

What to skip

Skip a mower sold with a pack under 4 Ah unless the lawn is tiny; it will stop before you do. Skip any 40V mower marketed for half an acre. Skip bargain brands with no spare packs or blades on sale, because a cordless mower lives only as long as its battery supply. Skip a mower with no single-lever height adjustment and no fold-flat handle. And skip the biggest deck you can afford for a small yard; a 21 inch mower on a 3,000 square foot lawn is a heavy machine you will not enjoy turning around the flowerbeds.