Professional Tool Reviews for Pros

DeWalt 40V Max String Trimmer Review

DeWalt 40V Max String Trimmer Head
PTR Review
  • Cutting Power 8.0
  • Run Time 9.5
  • Build Quality 8.0
  • Ergonomics 8.0
  • Value 8.0

DeWalt's entry into the 40V String Trimmer class is a great success. Well thought out design and solid performance characterize this model. It's a bit higher priced than some of its competition, though it comes with either a 4.0 or 6.0 amp hour battery.

Overall Score 8.3 (out of 10)

DeWalt DCST990H1 40V MAX Lithium Ion XR Brushless 15” String Trimmer

As a life long piston-head, DeWalt’s ‘Gas Performance Guarantee’ piqued my interest on the new DeWalt 40V Max String Trimmer. I’m a little old school, at least in my book, so replacing an internal combustion motor with a battery is just a few notches above borrowing another man’s tools and not returning them – heinous. When I got my hands on this trimmer, I had no intention of playing nicely. A crop of blackberry shrubs encroaching on my fence row would surely bring this trimmer to it’s knees…right?

DeWalt 40V Max String Trimmer Features and Build Quality

The first thing you notice out of the box is that this looks like a serious tool. No partial assembly required; it comes out of the box ready to work. The head of the trimmer is large, oblong, encased in metal, and it certainly appears as if it’s made to last. They also haven’t tried to get clever with the design by hiding bolts underneath plastic coverings. You can see the bolts run from the top of the motor straight through to attach the cutting guard. It’s a simple design, and I like that DeWalt didn’t sacrifice durability for aesthetics. It’s worth noting that the guard is incorporated into the motor housing and is not designed to be removed, which may be a deal breaker for anyone who prefers to work with the guard removed.

The brushless motor is attached directly to the trimmer head, and I’m a fan of this direct drive system. Less linkage means less torque loss through mechanical transfer. Since we’re on the topic and it pertains to DeWalt’s gas performance guarantee, lets talk a little about brushless motors. These motors are touted as ‘smart’ tools because they conserve energy when needed. Rather than a standard brushed motor which runs as fast as it can all the time, brushless motors adjust according to load. So if you’re trimming some grass around the play set, the motor will pull less charge from the 6.0 amp hour battery. Put the trimmer up against some 4 foot tall weeds, and the motor will pull more current. In addition, brushless motors have less parts than brushed motors, so they can be bigger, and generate more torque. No brushes also means less friction and more power to the drive assembly.

DeWalt 40V Max String Trimmer Battery Compartment

The battery housing in back is formidable. True it’s made of plastic, but the plates are thick and I can’t see myself doing anything involving normal wear and tear that would break them, so they work. I really like how the battery is protected from bumps and jolts. There are no concerns of hitting it on a fence post and breaking the electrical connectors. Inside the housing are guide rails along the top that help the battery slide in and match up with the electrical leads perfectly. Springs work against the locked battery, so when you release the latch the battery pops out an inch or so making it easy to grab.

In the locked position you have easy access to push a button on the battery to see how much juice is left. This housing also serves to keep the trimmer elevated off the ground thanks to a skid plate on the bottom.

The foam cushion around the auxiliary handle feels nicer than a hard plastic alternative, but I question it’s long term durability. Still, DeWalt was thoughtful in the design, if this handle ever wears out on you it would be a simple chore to remove and replace it with a new one. The squared off 3 sided design of this handle also makes it great for turning the trimmer on it’s side and using as a edger.

The throttle is controlled by a variable speed trigger which is very smooth and responsive. Directly in front of this trigger is a speed control switch. The low setting is designed to increase run time and the hi position provides accelerated RPM’s for heavier jobs. I found that all my work that was just around the yard could be done on the low setting which is great! Lithium Ion batteries aren’t cheap and they’re only good for so many power cycles, so the less you need to recharge them the better.

DeWalt 40V Max String Trimmer Speed Selection

In your hands the trimmer feels heavy, but not too heavy. DeWalt lists it at right around 14lbs. With the battery out it’s lopsided on the trimming end, but after a quick charge I threw the battery in back and the trimmer balanced out nicely.

Power is delivered via one of two options, both are 40V batteries, but it’s amp hours that really matter. For $299 you can pick up the 4.0 amp hour version, chuck in another $70 to the black and gold and you’ll get the 6.0 amp hour battery we tested. This the same battery used to power the DeWalt 40V Max Blower which will make it a great choice for buyers trying to stay on a consistent platform. As previously noted, the trimmer has a 15” cutting swath which we feel is critical for prosumers who want to make the switch to cordless OPE, but don’t want to sacrifice major features for battery convenience.

DeWalt 40V Max String Trimmer Fence Line

The line diameter is only .080”. I’d like to see this at .095” and up to be more in line with pro models that need string to last longer. Still the DeWalt 40V Max String Trimmer comes loaded with a good quality twist string designed to reduce engine drag and resist wear and it got the job done. It was easy to load the string in the spindle and the bump feed feature worked fine as expected. Nothing revolutionary, but it doesn’t need to be. One feature I would like to see on this, and every other trimmer, is an anchor point for a shoulder strap. Any prolonged use, which the 6.0 amp hour battery provides for, would certainly be aided by this simple to add feature.

DeWalt 40V Max String Trimmer Performance

The Task

Ok, so on to the bit that really matters. I used the new DeWalt 40V Max String Trimmer for about three weeks. I spent time trimming up the fence line, driveway, around and under swing sets and my shed. I recently purchased my home and judging by the heavy weed/shrub growth, several of the garden boxes had obviously gone unused for a while and made for a great test site to determine if I was really going to get gas power from an electric trimmer.

First Impressions

Starting the tool is simple—you just insert the battery until it clicks, grasp the safety lock-off lever and squeeze the trigger. There are no On/Off digital controls or “boost” settings. It just fires up and goes. There is no soft start on this tool either, it spools up almost instantly to ~5600 RPM on low and 6600 on high. It has a solid feel to it and it’s pretty quiet too. I could easily carry a conversation with my wife while trimming around the yard. The variable speed trigger was effective at being able to manipulate the RPM’s. I feel like I had great control over the DeWalt 40V Max String Trimmer.

DeWalt 40V Max String Trimmer Trigger

Initially I left the trimmer on low, wanting to see what kind of performance I could get. It turns out that I was perfectly happy with it’s ability to clean up around the yard on this battery conserving setting. The oblong head was easy to maneuver in and out of tight spots even though it’s a lot larger than some competitors. The relatively slim cutting guard may not be effective at keeping the grass clippings out of your shoes, but it made getting into tight spaces easy so I’ll take it.

High Stress

Now to put DeWalt’s gas power guarantee to the test. I found a nice thick tangled mess of weeds, flipped the speed control switch to high and went to work. The trimmer did clear out the brush, but it was only after several passes and some persistence on my part. There were spots in the weeds where the line spun and spun, but the weeds refused to go down. I felt like the motor couldn’t generate enough torque to cut down thicker plants, or perhaps the .080” diameter string just wasn’t up to the task. Either way, neither of these features can be changed.

DeWalt 40V Max String Trimmer Action

I’ve since used the trimmer several more times on tougher areas, clearing out those overgrown garden beds and each time this trimmer comes up just a little short of being able to blast right through tougher jobs that my 25cc two stroke never had trouble with. Of course, we don’t see anyone offering edger and brush cutter attachments on their lithium ion string trimmers, so you’ll notice the difference in these high stress applications. Edging around the patio, on the other hand, was an easy task for the DeWalt 40V Max String Trimmer and the 3 sided handle meant it felt comfortable in my hands during use.

DeWalt 40V Max String Trimmer Fence Line

Run time on the battery was impressive. In the three consecutive weekends that I used this trimmer I had to recharge the battery a grand total of 0 times. I was using this tool on it’s initial charge from day 1. I can’t say I timed my usage, but I have a 1/4 acre lot with a lot of landscaping beds, a shed, swing set, two patios, and it’s fully fenced in. I went around all of it all three weekends, including the inside and out of my fence line. A conservative estimate would be about 1 hour of use spanning 3 weekends and the battery indicated I still had 1 bar left when I finally gave in and put it on the charger.

DeWalt 40V Max String Trimmer Specs

  • Models: DCST990M1 (4.0 amp hour kit), DCST990H1 (6.0 amp hour kit)
  • Power Source: 40V Max Battery
  • Cutting Diameter: 15″
  • Line Size: 0.080″
  • Head Style: Dual line
  • Weight: 14.9 pounds
  • No Load Speed: 0 – 5600 RPM (low), 0 – 6600 RPM (high)
  • Warranty: 3 year
  • Price: $299 (4.o amp hour kit), $369 (6.0 amp hour kit)


This is a well thought out tool, and the DeWalt 40V Max String Trimmer is a great success for the company’s first shot at lithium ion OPE. The combination of features and feel far outweigh my need to take a few extra passes on the tougher scrub brush. Like other lithium ion trimmers, it comes up short on the run time that professionals need. However, if I’m buying a trimmer as a pro-minded homeowner, the undeniable convenience of battery power and zero maintenance makes buying this trimmer an easy decision.

Related articles

Makita ConnectX Lawn Care Equipment Video

Makita is making big strides in helping professional lawn care crews switch from gas to battery power. At the heart of their latest initiative is the ConnectX power supply—a 1200 watt-hour backpack battery that also fits on top of a self-propelled lawn mower. With the initial launch, there’s also a string trimmer and blower, and […]

DeWalt Vs Milwaukee Video | Thanksgiving Edition

Josh and Kenny planned to revisit our Milwaukee vs DeWalt one-hand reciprocating saw head-to-head. Unfortunately for the test (and fortunately for our appetites), they quickly lost focus and, well, you can see for yourself what happened. Still, it was highly entertaining for the rest of the office and the results were delicious. From all of […]

Notify of
Oldest Most Voted
Inline Feedbacks
View all comments

My 40 volt is going strong after 3 years or more. i would like to put a blade on it. Has anyone found a kit for this?

Darrell Wolf

why would i pay $250 for a battery powered trimmer then have to pay that much or more for a backup or replacement battery?? it woud be just as easy and probaby cost. less in the long run to just buy 2 trimmers. and alternate them.

James Lauritzen

I paid a lot for this item, because I was a De Walt fan. Used it maybe a dozen times before it started getting weaker and weaker, and the battery ran down faster and faster. It is so bad I’m just taking to the dump in my next load, even though it is still under warranty. I learned my lesson, which is that you can no longer trust De Walt to be quality stuff.


I have the same trimmer, and it has been working great, UNTILL last week when it acts like the motor is stuck in low power mode.
It hardly cuts regular grass let alone any weeds or heavier items.
Headed to repair shop, hope cost is not more than cost of machine.
I use Dewalt tools all the time they have been excellent, hoping this is just a small easy to fix problem.


wanting 40 volt chainsaw and weed trimmer but worried they will be phased out like other brands that have went back to straight 20 volts

Would love your thoughts, please comment.x