EGO POWER+ ST1521S review

We have not used this trimmer. What follows is every figure EGO publishes about the ST1521S, converted where conversion helps, and an honest account of the one number that holds it back — which is not a number about the tool at all.

The short answer

Everything EGO publishes

The kit is the problem, not the tool

It is worth separating the two findings. Drawing 4.67 watt-hours a minute is 31% more than the two most efficient trimmers here, and that is the tool. Shipping 140 watt-hours is the kit, and that is a purchasing decision you can undo by buying a bigger pack. Our bare tool or kit guide covers when that makes sense.

What the evidence says in its favor

• POWERLOAD. Reloading line is the job that makes people stop using a trimmer, and this is the only head in our registry that automates it. Our trimmer maintenance page covers what the alternative involves.
• A lifetime shaft warranty, published. The shaft is the part that gets levered against a fence post, and no other trimmer we hold specs for warrants any component for life.
• 0.095 in line, the heavier of the two gauges in our registry, which lasts longer against brick, wire and concrete.
• A split shaft, so the powerhead takes EGO attachment heads — see multi-head systems.
• Five-year tool warranty, matched only by EGO's own products here.

What is genuinely against it

• Thirty published minutes, less than half the RYOBI's 67.
• The highest draw of the four at 4.67Wh per minute. A bigger pack fixes runtime, not efficiency.
• A 50 minute recharge against a 30 minute runtime. Greenworks' ST80L210 recharges in 30 against a 45 minute runtime, which makes two packs continuous; this one does not.
• No published weight and no published motor speed. On a tool held at arm's length for an hour, the weight omission is the one that stings.
• A fixed 15 inch swath, where RYOBI publishes an adjustable 15 to 17 and Greenworks 14 to 16 — adjustability matters along a fence.

Where it sits against the other three

Read down the runtime column and this trimmer is last by a wide margin. Read down the equipment column — automatic winding, heavy-gauge line, a lifetime shaft warranty — and it is first. Both readings are correct, and which one governs depends entirely on whether you are buying the kit or buying the tool.

The recharge figure nobody looks at

On the EGO platform this matters less than it looks, because a 7.5Ah or 10.0Ah pack changes the runtime side of the equation rather than the charging side. But on the kit as sold, two batteries do not buy you a continuous afternoon.

What POWERLOAD is worth, honestly

Automatic line winding is the feature people buy this trimmer for, so it deserves a clear account rather than a bullet point.

• What it replaces: opening the head, winding line onto a spool in the right direction, seating it in the notches and reassembling — the job our trimmer maintenance page describes by head type, and the one that makes people put a trimmer down for a season.
• Where it pays most: jobs that eat line. A fence line, a brick edge or a gravel border empties a spool far faster than open grass — see trimmers for fence lines.
• What EGO does not publish: how much line the head holds, how long a full load lasts, or whether the mechanism tolerates the cheaper line most people actually buy. None of that is on the product page.
• What it does not change: line consumption itself. The head reloads more easily; it does not use less.

The shaft warranty, and why it is unusual

A string trimmer shaft takes loads nothing else in a cordless kit does: it gets levered against fence posts, used to part shrubs, leaned on, and dropped. Carbon fiber is stiff and light, and it is also the material people worry about cracking.

EGO publishing a lifetime warranty on exactly that component is the clearest signal available that it expects the shaft to outlast the tool, and it is the only lifetime term on any component of any product in our registry. It is worth weighing against the things this page has criticized, because a warranty is a published commitment rather than a marketing adjective.

The split-shaft design has a second consequence: the powerhead takes EGO attachment heads, so the same motor and battery can run an edger or a pole saw — see multi-head attachment systems.

Who should buy it

Buy it if you already own EGO 56V packs, because then the kit battery is irrelevant and you are buying the best-equipped head in the category with a lifetime shaft warranty. Buy it for a small or medium lot where 30 minutes is plainly enough. Skip the kit as your entry into the platform if you have a large yard — our large-yard trimmer page ranks on exactly the figure this kit is weakest on.

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The verdict, in one paragraph

The best-equipped trimmer head in our registry attached to the smallest battery in our registry. POWERLOAD, heavy 0.095 in line, a carbon fiber split shaft with a lifetime warranty and five years on the tool — against 140 watt-hours, 30 published minutes and a recharge longer than the runtime.

That makes it an excellent tool and a poor kit. If you are already on the EGO platform with a larger pack, the criticism evaporates entirely and it becomes the easy recommendation. If this would be your first EGO purchase and you have a large yard, buy the battery you need rather than the one in the box.

What we cannot tell you

We have not used this trimmer. EGO publishes no weight, no motor speed and no conditions for the 30 minute claim — line length, grass type and trigger position all change it. We cannot tell you how POWERLOAD behaves with a worn spool, how the split shaft joint holds up, or what the tool weighs with a 10.0Ah pack fitted.