How long do electric lawn mower batteries last?

"How long does the battery last" is two questions wearing one sentence. One is about minutes and has a precise answer. The other is about years and mostly does not, because the industry does not publish the data.

Question one: how long per charge?

Two useful things fall out of that table. First, the spread in per-minute draw is real but modest: 6.0 to 9.7Wh per minute across four 21-inch mowers. Second, every one of these claims is a best case — dry grass, cut regularly, at a sensible height. Thick, wet or overgrown grass raises the draw, sometimes sharply.

That is the whole calculation. It is why we keep saying to size the pack to the lawn rather than to the price tag — the full ten-year version lives in the cost calculator.

Question two: how many years?

Read that table the way a manufacturer's finance department reads it. A warranty term is a company's own estimate of how long a component survives, priced so that honoring it is cheaper than the sales it wins. When Greenworks puts four years on a battery and EGO puts three, Greenworks is making the more expensive promise.

Notice too that EGO warrants the tool for five years and the pack for three. That gap is the industry telling you which component it expects to fail.

What we genuinely do not know

This is where most articles on this question start estimating, and we are not going to.

• We do not know the cycle life of these packs. None of the four brands here publishes a cycles-to-80%-capacity figure for outdoor packs, the way electric vehicle manufacturers do.
• We do not know the cell chemistry per model. Different lithium chemistries age very differently, and none of these product pages says which is inside.
• We have not run any of these packs for five years, because we have not run any of them at all. We have not tested these units and we say so on every page.

What we can tell you is that the general behavior of lithium cells is well established outside this industry: heat accelerates degradation, storage at full charge accelerates it, deep discharges are harder on a cell than shallow ones, and calendar age matters even for a pack that is never used. Those principles are not brand-specific and not in dispute. Applying them is the rest of this page.

Making a pack last

1. Do not store packs in a hot shed over summer. Heat is the single largest controllable factor. A garage wall beats a metal shed roof.
2. Do not store at 100% for months. If a pack is going into winter, running it down to roughly half and leaving it there is gentler than leaving it full.
3. Let a hot pack cool before charging. Straight off a mower in August, it is the worst moment to push current back in. Most chargers wait for you; the ones that do not, you should.
4. Prefer shallower discharges where it is convenient. Two packs each doing half the lawn is gentler than one pack doing all of it, which is a quiet argument for the two-pack kits.
5. Charge indoors, at room temperature, and not on a freezing concrete floor in February.

When to replace

There is no calendar answer, and any page that gives you one is guessing. There is a practical one.

Time your mow now, while the pack is new. Write the number on a bit of tape on the charger. A healthy 420Wh pack finishing your lawn in 38 minutes today is your baseline. When that same lawn needs a swap partway through, the pack has lost enough capacity to matter to you specifically — which is the only threshold that counts.

At that point you have a real decision, and it is a platform decision as much as a battery one: a replacement pack on a platform with four other tools on it is an easy purchase, and on a platform with one tool on it is often the moment people switch brands. That asymmetry is exactly why the platform choice is the one that matters.