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Black+Decker LST540B Review

If you are looking for a light-duty weed eater that won't demolish your budget, the LST540B is an excellent option
black+decker lst540b cordless string trimmer review
Price:  $220 List
Manufacturer:   BLACK+DECKER
By David Wise, Michelle Powell, and Jenna Ammerman  ⋅  Sep 4, 2019
  • Weed Eating - 30% 5.0
  • Ease of Use - 30% 7.0
  • Battery - 25% 5.0
  • Noise - 15% 9.0

Our Verdict

Discontinued - Fall 2019
Great value
Practically silent
Easy to use
So-so weed eating performance
Mediocre battery life
As of Fall 2019 the Black+Decker LST540B is no longer available from the manufacturer.

If your weed eating needs aren't particularly intense and you aren't looking on spending a whole lot on a new cordless string trimmer, then the Black+Decker LST540B is a fantastic option. This weed eater isn't the most powerful of the group and doesn't have an exceptionally long battery life but it has more than enough oomph for typical weed eating applications. On top of that, it is exceptionally easy to use and incredibly quiet for these products.

Our Analysis and Test Results

The Black+Decker LST540B is particularly great for smaller users, as it is one of the lightest and easy to handle string trimmers. It does have a relatively short reach, so it can actually be a bit more difficult to use for taller people.

Performance Comparison

black+decker lst540b cordless string trimmer review - the lst540b is a great budget buy.
The LST540B is a great budget buy.
Credit: Jenna Ammerman

Weed Eating

First, we graded the performance of each of these weed eaters at their namesake task: weed eating. This accounts for 30% of the final score for each string trimmer, based on how well each product cleared vegetation, how easy it is to make detail cuts, and how it handled particularly thick sections of grass and weeds. Unfortunately, the LST540B couldn't really compare to the top-tier models, earning one of the lower scores of the group for its so-so performance.

This weed eater from Black+Decker does a good job at clearing dry or soft grasses or weeds but it can get bogged down when trying to cut through burlier vegetation. It even does alright on taller or particularly thick-stemmed weeds and plants — as long as they aren't particularly dense patches.

black+decker lst540b cordless string trimmer review - we found the overall weed eating performance of the black+decker to...
We found the overall weed eating performance of the Black+Decker to be lackluster at best.
Credit: Jenna Ammerman

We found that the guard on this trimmer can get caught up in dense patches of vegetation, pulling the trimmer off course and into the ground — usually causing a tangled mess that we would have to stop and fix before continuing. Overall, this trimmer is underpowered compared to the top models and we wouldn't pick this weed eater for anything more than light-duty yard maintenance. The guard is also quite large and can get in the way whenever you are trying to do detail work or edging.

black+decker lst540b cordless string trimmer review - the guard on this trimmer gets caught when cutting through patches...
The guard on this trimmer gets caught when cutting through patches of tall grass.
Credit: Jenna Ammerman

Ease of Use

The LST540B redeemed itself in our next set of tests, earning a much better score for being one of the most convenient and user-friendly string trimmers of the group. This metric is also responsible for 30% of the total score and is based on how much work it is to dispense more string or replace it, how comfortable it is to hold and carry around, and the effectiveness of the guard.

The Black+Decker has an automatic line dispensing mechanism, so it will automatically sense when you need more string and dispense it accordingly. It has one of the most straightforward systems when it comes to replacing the line. The LST540B weighs in at a little more than 7 lbs., making it one of the lightest string trimmers we have tested so far.

The head is just a little bit heavier than the battery end, which holds the trimmer at an almost ideal handle for use, but it can be a bit funky to carry one-handed while holding on to the grip.

black+decker lst540b cordless string trimmer review - the guard does do a good job of blocking flying debris but gets in...
The guard does do a good job of blocking flying debris but gets in the way during detail work and edging.
Credit: Jenna Ammerman

The handle is made of hard molded plastic that isn't the most ergonomic to hold but isn't overly unpleasant. However, it definitely isn't the grippiest handle, so you are going to want to make sure you have a good hold on it while weed eating. The handle does protrude out far enough to get in the way for detail work when holding the trimmer vertically.

You can also end up hunched over when doing detail work with the LST540B's shorter reach, making it particularly cumbersome to use if you have a taller stature. The guard on this machine is exceptionally large compared to the rest, doing a great job of blocking debris from getting thrown around but it does routinely interfere when trying to do detail work as well.

black+decker lst540b cordless string trimmer review - the lst540b is lightweight and easy to hold.
The LST540B is lightweight and easy to hold.
Credit: Jenna Ammerman

Battery Life

Our next testing metric dealt with the battery life of each of these cordless tools, which is responsible for 25% of the final score for each product. We started each trimmer with a completely charged battery, then timed how long each one ran under no-load conditions to compare their performance side-by-side. Additionally, we awarded extra points to models that multiple speed modes, as this lets you extend the effective battery life by reducing the power for easy to cut grass and weeds and throttling up when you need to make it through denser material. The Black+Decker did fairly well, earning a middle-of-the-road score for its so-so performance.

The LST540B lasted for about 37 minutes before dying in our test when spinning freely, with this runtime reducing depending on the amount and thickness of the vegetation you are cutting through.

This string trimmer only has a single operating mode and is so relatively underpowered to the top models that its standard speed mode seems similar to the low power mode on the top-tier trimmers.

black+decker lst540b cordless string trimmer review - the lst540b has an average runtime in our tests.
The LST540B has an average runtime in our tests.
Credit: Jenna Ammerman


For our fourth and final metric, we scored each string trimmer on the amount of sound that they produced, which accounts for the remaining 15% of the final score for each product. The majority of the score for each product is based on the number of decibels (dBa) recorded by our sound meter from a distance of 36" away but we also had several judges rate and score how distracting the sound is to account for any particularly grating or high-pitched tones produced. The Black+Decker LST540B did very well, earning one of the highest scores of the entire pack when it came to sound levels.

We only recorded sound levels of around 87 dBa at this distance from the Black+Decker, which puts it well on the quieter end of the spectrum for string trimmers.

However, our judges did feel that the sound from this weed eater can be a bit on the whiny side but isn't too irritating.


All in all, it's hard to beat the Black+Decker when it comes to being a bargain buy. It isn't the best for heavy-duty use but if you are looking for a decent product that won't drain your bank account, then the LST540B is an excellent choice.


The LST540B is a lightweight and quiet weed eater that is perfect for light-duty work. It lacks the raw power of the top models and gets bogged down in thicker vegetation but it still usually can cope with smaller lawn maintenance without too much difficulty. This cordless weed eater is a great option if you need a decent string trimmer without cutting into your savings a huge amount.

David Wise, Michelle Powell, and Jenna Ammerman

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