GreenWorks G-MAX 40V Twin Force Mower Review Reviews

GreenWorks G-MAX 20” 40V Cordless Twin Force Mower: Product Review

GPR Recommendation

Ease of Use
Final Thoughts

Overall, this is a nice replacement for a conventional gas mower

Overall Score 4.3

Available on Amazon

Buy It


Every year there are more battery-powered mowers on the market, and they’ve gone from being a curiosity to a mainstream option in the lawn care space. Mowers in general have come a long way since I started my first business (Whitehaven Lawn Mowing) at age 12 (it put me through college and I mowed a LOT of lawns!). So it I was looking forward to testing the latest cordless lawn mower designs.

Setting Up The Mower

The GreenWorks G-MAX mower arrived in a box with all of the parts well packaged so there was no shifting or damage during transport.

Included in the box are the following:

  • Twin Force Mower
  • Rear discharge bag
  • Mulching plug
  • Owners manual
  • 1 4Ah 40V battery
  • 1 2Ah 40V battery
  • Battery charger

The mower was ready to go out of the box – all I had to do was adjust the handle bar from the storage/transport position to the mowing position by loosening a lever, moving the handle into position, and then flipping the lever back to the closed position. The handle can be just as easily folded back to make it more compact for storage.

GreenWorks mower in box

The mower is neatly and securely packaged and needs no assembly.

When the mower arrives, the mulching plug is already installed in the slot at the rear of the mower. If you don’t want to mulch your grass, you’ll need to remove this plug before using the mower – just pull it out and store it somewhere safe.

The instruction manual is clear and detailed.

About Lithium-Ion Batteries

  • Do not have a “memory” and can be charged at any time.
  • Once the charging light turns green (on the battery charger) remove the battery from the charger.
  • Unplug charger when not in use.
  • Fully charge batteries when placing them in storage.
  • Batteries will eventually need to be replaced.

See our full Q&A on Li-ion batteries here.

About the Li-Ion Batteries

Inside the box was a battery charger and two 40V lithium-ion batteries. The two batteries are different; one is a 2 Ah and the other a 4 Ah. Don’t worry, it’s not a packing mistake and it doesn’t matter which slot each battery goes into on the mower. (Note: The 19” model (25312) comes with two 4 Ah batteries)

The batteries and charger used in the G-MAX mower are compatible with any other tools that use the GreenWorks G-MAX 40V Li-Ion System.

Eventually, the batteries will need to be replaced (this is the case with all Li-ion batteries). Greenworks gives no recommendation about when you should do this, but Li-ion batteries typically last about 3 years.

>> See our FAQs About Li-Ion Batteries

Charging the Batteries

Before using the mower, be sure the batteries are fully charged. I found that they charged from fully depleted (0%) to fully charged (100%) in about 1 to 1.5 hours, depending on the Ah. Charge time was less when there was still some charge left on the batteries.

Greenworks charger

Keep the battery on the charger until the green indicator light on the right turns on.

Each battery has a status light on one end showing how much charge it has left. Depress the green button to the right of the status light bar to get it to light up.

When you’re ready to mow, the batteries are easily installed into the mower – just slip one into each of the slots in the covered battery bays. The batteries have a depressed locking mechanism to keep them in place while in use and then quickly release them for charging and storage.

When not in use, remove the batteries from the mower and store them inside.

Testing the G-MAX Cordless Twin Force Mower

I put the GreenWorks G-Max mower through its paces on two large lawns made up of either fescue or St. Augustinegrass. After several mowings at different heights, I found a lot to like about this mower, plus a few things I’d like to see improved. Below are my observations and recommendations, as well as a video review so you can see it in action.

Long Battery Run Time

One of the big questions everyone has about a battery-powered lawn mower is how long it’ll run before you need to recharge the battery. The convenience factor of not needing to use gas or drag around an extension cord only goes so far if the battery runs out quickly!

So I was pleasantly surprised to find that the run time when using the recommended 4.0Ah and 2.0Ah batteries was about 1 hour and 15 minutes. That’s more than enough time to mow a typical suburban lawn.

An interesting feature on the G-MAX Twin Force mower is the automatic battery switchover. When you start mowing, power is pulled from only one battery. When that’s depleted, power is pulled from the second battery.

batteries on GreenWorks mower

Two battery bays on the GreenWorks G-Max Twin Force mower.

This also allows you to run the mower on just one battery at a time. Although I don’t recommend this, it’s possible to put one battery in the mower and keep the other on the charger until the first battery runs out. Of course, you then have to swap out the batteries.

One thing that’s missing is a battery status indicator on the mower handle, as found in some other cordless mower models. As it is, you have to stop the mower, open each battery compartment and depress the indicator button to see how much life is left in each battery.

Greenworks battery indicator

The only way to tell how much “juice” is left in the batteries is to press the green button on the batteries.

Simple to Start the Mower

The G-MAX Twin Force mower has a nice dual-stage safety feature to prevent accidentally starting it. First press the button on the right handle to activate the batteries, and then hold down the safety bail handle to start the blades.

simple start on GreenWorks mower

Start the GreenWorks mower by holding down the start button and then gripping the safety bail against the handle.

Excellent Mulching & Mowing

The GreenWorks G-MAX Cordless Twin Force Mower has two separate cutting blades that rotate in different directions (they both rotate inwards, effectively shooting cut grass backwards into the grass catcher on the back of the machine).

twin blades on GreenWorks mower

The twin blades move in opposite directions to shoot grass out the back of the machine.

This resulted in excellent mulching when the mulching plug was inserted and a very clean cut across the entire 20-inch cutting deck in both the mulching and non-mulching cutting modes. The mulching blade chopped grass on both fescue and St. Augustinegrass lawns into such small pieces that no grass clippings were visible when I’d finished mowing. Even in longer grass, there were no visible clippings and the cut was even across the entire lawn surface.

The large (55L capacity), rear-mounted grass catcher has mesh sides, a hard top and semi-hard bottom. There’s a small flap on top that lifts up when the bag is getting full, indicating that it’s time to empty it.

GreenWorks has built their “SMART CUT technology” into the G-MAX mower. Although I couldn’t test it directly, GreenWorks claims that it adjusts power or runtime based on the thickness of your grass. All I can say is that it worked extremely well on both fine and thick grass of different heights.

greenWorks mower cuts lawn

Think a cordless mower can’t cut a large lawn? Think again! The GreenWorks managed this lawn with plenty of run time left on the batteries.

Easily Adjustable Cutting Height

Cutting height on the G-MAX mower can be set at 5 positions, ranging from 1 ¾” to 3 3/8”.

The mowing deck height is easy to adjust with the lever on the top of the mower, although I did find that it was a little cumbersome moving the lever upwards (increasing the cutting height) and found that it worked better if I also lifted up on the body of the mower (obviously you shouldn’t do that with the batteries installed as your fingers would be dangerously close to the blades!).

It would be easier and more convenient if GreenWorks included a handle at the center of the mower so you could lift it when needed (for example, when transporting it in the back of a vehicle, raising the cutting height or just moving it into position when mowing).

GreenWorks mower adjustable height

The cutting height can be adjusted into 5 positions by moving the levers.

Comfortable and Maneuverable

There’s a layer of foam covering the handle grips, dampening any vibration and making it comfortable to push the mower around even when the safety bail is engaged. It doesn’t take much pressure to hold down the safety bail so my hands didn’t get tired from gripping it.

However, the foam covering isn’t very thick and can easily wear or rip. It would be better if it was made of sturdier material for longer life. Of course, you could always use the “universal fix-it solution” – duck tape – wrapped around the handle to protect the foam. But it seems silly to have to go to that extreme on a machine that costs around $400….

Another potential negative is the fact that the handle height isn’t adjustable so it may feel a little short for taller individuals, or too high for shorter people.

The G-MAX mower feels very similar to a traditional gas-powered mower when in use. Still, it’s relatively lightweight (42.5 lbs – one person could lift it without any help) and very maneuverable.

Part of what makes it easy to maneuver is the size of the wheels, with larger 10” wheels in back and 7” wheels up front.

Limited Warranty

The mower itself is warranteed for 4 years (with proof of purchase) against defects in materials, parts or workmanship.  This warrantee is valid only for units which have been used for personal use (they haven’t been hired or rented for industrial/commercial use), and that have been maintained in accordance with the instructions in the owners’ manual.

As usual, normal wear and tear, routine maintenance items and normal deterioration of the exterior finish aren’t covered.

The batteries carry a 2-year warrantee against workmanship and materials, as long as they’ve been charged in accordance with the operator’s manuals directions and regulations.

Safety First

An important safety feature on lawn mowers is the hard strip across the underside at the rear of the mower. This is intended to stop a toe or other object from inadvertently getting chopped to pieces by the blades when moving backwards. (Editor’s Note: Mowing backwards is never recommended by lawn mower manufacturers as it increases the risk of stumbling, running over something, or injuring yourself.) However, on the Twin Force mower this strip is a very flexible piece of rubber that does nothing to protect you or the mower. I’d have liked to see a stronger protection device here.

This is an electrical device and should not be used in wet weather or severely wet lawn conditions as you risk getting a nasty electrical shock.

As with all lawn mowers, wear safety glasses, sturdy boots and, although the G-MAX is relatively quiet (at least compared to a gas mower), I recommend hearing protection as well.


Overall, this is a nice replacement for a conventional gas mower. It has plenty of power, excellent mulching capability, a long enough run time to mow most suburban yards, a 20″ cutting deck, and good maneuverability and balance. There are a few small drawbacks that you wouldn’t expect in a mower at this price point, such as the flimsy foam padding on the handles and the lack of a handle-mounted status indicator. I’ve also seen reports of the cable between the start switch and safety bail stretching to the point that the machine becomes inoperable, although this hasn’t happened on the machine I tested (yet).

Where To Buy

The Greenworks G-Max 40V Cordless Twin Force Mower (with batteries and charged included!) can be most easily be purchased on Amazon.

Replacement batteries and chargers are also available on Amazon.

And now over to you – Have you used a cordless mower? How did it work? Let us know in the comments below!

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Disclaimer – GPReview would like to thank GreenWorks for giving us a free sample to review. There was no expectation that it would be a positive review and we received no compensation for writing it. All opinions expressed here are those of the author based on personal experience using the product.

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6 Comments on GreenWorks G-MAX 20” 40V Cordless Twin Force Mower: Product Review

  1. David laverack

    Hi I have just purchased a greenworks 25137/25367 mower, but I find it does not cut short enough, are there any modifications to lower the blades.
    It feels more a grass pasture mower than a lawn mower?
    Best regards David.

    • Hi David, I’m not sure why you’re not getting a short enough cut. It’ll cut down to just below 1.5 inches (35mm) which is really short. Most grass should be cut higher than that. (as the manual says “The average lawn should be between 38mm and 51mm during cool months and between 51mm and 70mm during hot months.”) The height adjustment lever at the side of the mower should be easy to set to the correct height. I definitely wouldn’t recommend making any modifications to the machine!

  2. S Slater

    Yes, I agree with Monica. Just purchased this lawnmower and doesn’t cut the grass short enough.

Comments are closed.