What's inside
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A Spear & Jackson cordless lawn mower is one of the better-value ways to cut a small-to-medium UK garden without a cable, and for most buyers the 42cm 40V model is the pick of the range — wide enough for lawns up to roughly 500 m², light enough to lift, and part of a battery platform that also powers a trimmer, hedge cutter and the Spear & Jackson lawn edger. Below is what actually matters before you buy: cutting widths, honest runtime figures, height adjustment ranges, and where the spares come from.
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The cordless range at a glance
Spear & Jackson sells battery mowers on two separate platforms: a 24V system for the smallest gardens and a 40V system for everything else. If you’ve been hunting for a Spear & Jackson electric lawn mower, note that the corded models still exist as budget options, but the Spear & Jackson lawnmower cordless line-up is now the core of the range. Approximate published specifications:
| Model | Battery platform | Cutting width | Grass box | Height range | Weight | Lawn size guide |
|---|---|---|---|---|---|---|
| 32cm cordless rotary | 24V | 32 cm | ~30 L | 5 positions, ~25–65 mm | ~8.5 kg | Up to ~200 m² |
| 37cm cordless rotary | 40V | 37 cm | ~40 L | 6 positions, ~20–70 mm | ~11 kg | ~300 m² |
| Spear & Jackson 42cm cordless lawn mower | 40V | 42 cm | ~50 L | 6 positions, ~20–70 mm | ~13.5 kg | ~400–500 m² |
| 46cm self-propelled | 40V | 46 cm | ~55 L | 6 positions, ~20–75 mm | ~17 kg | ~600 m² |
Exact figures vary slightly by bundle and year, so treat these as representative and check the listing for the specific kit you’re buying. The more important point is the two-platform split — a detail many listings bury.
Runtime per charge: the honest numbers
Manufacturer runtime claims assume short, dry grass. In practice, a Spear & Jackson battery lawn mower running a 40V 4.0Ah pack (roughly 160Wh of energy) will give you:
- ~35–45 minutes on a weekly-cut lawn kept at 40–50mm
- ~25–30 minutes on grass that’s grown out or slightly damp
- ~15–20 minutes on the first cut of spring when you’re dropping two height levels
What does that cover? A worked example on the 42cm model: your effective cutting width after overlap is about 37cm. At a comfortable walking pace of ~0.9 m/s, that’s roughly 1,200 m² per hour in theory. Factor in turnarounds, grass box emptying every few minutes on a lush lawn, and slopes, and a realistic per-charge figure lands around 450–550 m² — which is exactly why Spear & Jackson rates that model for ~500 m² lawns. The maths genuinely checks out.
One critical buying check: the same mower is sold as a bare unit, with a 2.0Ah battery, or with a 4.0Ah battery. A 2.0Ah pack halves every number above. If your lawn is over ~300 m², either buy the 4.0Ah kit or budget for a second battery (~£40–£90 depending on capacity, general market range).
Cutting width and height adjustment in practice
All the 40V models use a single-lever height adjuster covering roughly 20–70mm in six positions. Two things worth knowing before you mow:
- 20mm is shorter than most lawns need. It’s useful for a tight summer cut on flat, fine turf, but on a bumpy lawn it scalps easily. Most owners will live on positions 3–4 (35–50mm).
- The deck is rotary with no rear roller — these mowers won’t produce stripes. If stripes matter, you’re shopping in a different category.
- Cutting width trades off against storage. The 42cm deck shaves a few passes versus the 37cm, but adds ~2.5kg and a bigger footprint in the shed. All models have folding handles, though.
Which Spear & Jackson lawn mower fits your garden?
| Your situation | Best fit | Why |
|---|---|---|
| Small lawn under 200 m², limited storage | 32cm 24V | Cheapest entry, ~8.5 kg, stores on a shelf |
| 200–400 m², weekly cut, flat | 37cm or 42cm 40V | One 4.0Ah charge finishes the job |
| 400–600 m², or sloped/uneven ground | 46cm self-propelled | Drive system removes the pushing effort |
| Already own Spear & Jackson 40V tools | Bare-unit mower, any deck | Batteries swap across the 40V garden range, including the lawn edger |
| Want lightest possible mower for mobility reasons | 32cm 24V | Nearly half the weight of the self-propelled |
Spare batteries and replacement blades: where to source them
Two hard rules first. The 24V and 40V batteries are not interchangeable — different voltage, different mounting. And second batteries are best bought on the platform you already own; mixing platforms doubles your charging clutter for no benefit.
For genuine spares, the sensible channels are:
- The UK retailer that sold you the mower — most stockists of the range also list 40V spare batteries and chargers separately.
- Spear & Jackson’s own spare-parts service via the manufacturer’s website — the reliable route for blades, replacement grass boxes, handle fixings and chargers.
- Pattern (compatible) blades — widely available at lower cost; match the blade length to your deck (e.g., a ~42cm blade for the 42cm model) and check the centre hole fitting. Expect roughly £12–£25 for a blade, versus £40–£90 for batteries, as general market ranges.
Ownership realities: what wears and what to avoid
Rotary mowers are mechanically simple, so the wear list is short and predictable:
- The blade dulls first — expect to sharpen or swap it once a season, or sooner if you hit stones. A blunt blade tears grass rather than cutting it, which is the main cause of a brown-tipped lawn.
- Battery capacity fades after roughly 3–5 years of regular use. Store packs at 40–60% charge over winter, in the house rather than a freezing shed — storing a lithium pack flat or frozen is the most common way to kill it early.
- Folding handle clamps and grass box clips loosen over time; check them at the start of each season.
- The deck needs scraping after damp cuts. Wet clippings packed under the deck are the single biggest cause of terrible runtime and stalled motors — clean it, and don’t mow wet grass unless you have to.
Blade swap takes ten minutes: remove the battery first (always — the motor can spin on a stalled blade), tip the mower on its side with the air path up, crack the centre bolt with a socket, and torque the new bolt down firmly. A loose blade is genuinely dangerous; an overtightened one makes next year’s job miserable.
Quick answers
Can I use a 24V battery in a 40V Spear & Jackson mower? No — the two platforms share nothing. Stay within one voltage system.
Does the same battery power the lawn edger? On the 40V side, yes — the mower, grass trimmer, hedge trimmer and lawn edger share packs, which is the strongest argument for buying into the platform rather than a single tool.
Is a second battery worth it? If your lawn exceeds ~350–400 m² or you often cut grass that’s grown out, yes. It’s cheaper than a mower upgrade and doubles as a spare while one pack charges.
Do these mowers mulch? Most Spear & Jackson rotaries are collection-focused; check whether the specific model includes a mulch plug if that matters to you.
Verdict
The Spear & Jackson cordless lawn mower range wins on value, not on premium features — no stripes, no app connectivity, just competent rotary cutting at prices typically well below the big-tool brands. For lawns up to ~500 m² the 42cm 40V model is the balanced choice; go smaller for tiny gardens, and step up to the self-propelled 46cm if slopes or size make pushing a chore. Buy the 4.0Ah kit, keep the blade sharp, and it’s an easy recommendation.