Dewalt lawn mower flashing red light

Dewalt Lawn Mower Flashing Red Light: Solved!

Easy to use, quiet, and other great features make the Dewalt lawn mower popular. 

However, it does not prove that this mower is free of problems. There are some problems that this mower’s users often face. Red flashing lights are one of them. 

So, why Dewalt lawn mower flashing red light

The main cause of flashing red light is low or dead batteries. To solve this problem, you must fully charge the battery. Moreover, using incompatible batteries can trigger the appearance of red light. It is crucial to use a Dewalt-compatible battery, such as the Dewalt 20v Lithium Ion battery, to avoid compatibility issues. If the battery is defective, it should be replaced, as a faulty battery can also be responsible for the flashing red light.

Knowing the reasons and getting a glimpse at the solution won’t be enough. For a detailed explanation of the solution, read the entire article.  

Dewalt Lawn Mower Flashing Red Light: Possible Reasons And Solutions

If your Dewalt lawn mower flashes a red light, this could be due to multiple reasons. In order to determine if the red light can be fixed on your own, you need to understand the specific causes. 

Low or dead battery Battery voltage should be 12.6
Incompatible batteryUse batteries with 20v Lithium Ion.  
Defective battery Change the battery 
Problematic charger Replace or contract with customer support assistance 

It’s time to discuss the reasons and solutions in a broad manner. 

Reason 1: Low Or Dead Battery

The first leading reason for flashing red lights is having a dead or low battery. If the lawn mower’s battery is low or dead, it may not receive enough power to operate.

battery is low or dead

The red flashing light serves as a notification that the mower is unable to function. Because an inadequate power supply is going on.


The first thing, you need to do is connect it to the appropriate charger and allow it to charge fully. Once the batteries are charged, the red flashing light should stop, indicating that the battery is now providing adequate power. 

However, if the battery fails to hold a charge even after recharging, you need to replace the battery. You can collect the new battery from the authorized dealer.  

One thing more, a fully charged battery isn’t the solution to all problems. Because sometimes the battery doesn’t work even is fully charged.  

Reason 2: Incompatible Battery

Another significant reason is not having a compatible battery. In order to work properly, Dewalt lawnmowers require specific battery models.  You may not be able to power your mower if you use an incompatible battery. 

Therefore, the red flashing light is a warning that the battery can’t provide adequate power due to the voltage mismatch.


To get over the situation, you need to ensure that you are using a Dewalt 20v Lithium Ion battery.

Incompatible Battery

Also, you can use a Dewalt FLEXVOLT battery. These are the most compatible batteries with the lawn mower.  

Reason 3: Defective Battery

Another significant reason is having a defective battery. A defective battery can’t hold a charge. Dewalt batteries lack a comprehensive Battery Management System (BMS) and cannot cut off power when it’s low. 

It is the responsibility of the tool to stop draining power. However, it appears that the mower is not properly monitoring the batteries. It could be either a lack of individual battery monitoring or some other anomaly. 


Since the battery lacks a BMS, it’s important to closely monitor its usage. Keep an eye on the battery’s charge level and usage time. It will prevent over-discharging or overloading the battery.

Also, you should avoid using the battery until it is completely drained. Because this can lead to irreversible damage to the battery. 

If still, the problem persists, you need to contact the manufacturers. Otherwise, you need to replace the battery. 

Reason 4: Faulty Charger

A problematic charger can also initiate the problem. If the charger is not working properly, it may not be able to charge the batteries or may even damage them. If you suspect that the charger is defective, you should contact Dewalt for assistance 


Ensure that you use a charger specifically designed for your battery model. Avoid using generic chargers that may not provide the appropriate charging voltage. Using the correct charger can help optimize the battery’s performance and prolong its lifespan.

Tips to Prevent Flashing Red Lights on Dewalt Lawn Mower

To prevent flashing red lights on your Dewalt lawn mower, consider the following tips:

  • Always make sure that the batteries are inserted correctly. 
  • Don’t forget to keep cleaning the battery contact. In order to remove corrosion, you can use vinegar solution and WD40 spray.
  • Try charging the battery in a different location. Because Dewalt batteries can’t get charged past two bars if you charge them in the same location. 
  • Remember one thing do not allow the batteries to fully discharge before recharging them. Also, don’t overcharge the battery. 
  • Also, battery connections should be secured and tight. A loose connection can disrupt the power supply and cause the red light to flash. Before each use, double-check the battery connections.

Frequently Asked Questions (FAQs):

Why is my Dewalt Lawnmower isn’t starting?

The Dewalt lawnmower doesn’t start due to an incorrectly installed battery and insufficient battery power. You need to charge and install the battery perfectly. Also, a hot battery can cause your mower to shut down and not start. You can prevent this by cleaning the vents on your mower. Before trying to start again, let your battery cool down.  

Why is my electric lawn mower losing power?

Accumulated dirt and debris in the mower blade housing are the primary factors leading to power loss in electric lawnmowers. Grass clippings and dust can accumulate within the enclosed area where the mower blade is located over time. Gradually, this mixture solidifies and resembles concrete in density.  

Can an electric mower overheat?

Yes, an electronic mower can be overheated. One of the prevalent causes of mower overheating is often blocked cooling fins. Grass and debris from lawns or fields can easily enter cooling fins, causing this issue. A restricted air circulation leads to inadequate cooling of the engine, which leads to overheating. Also, low engine oil can lead to this issue. 


I hope you got to know why your Dewalt lawn mower flashing red light

The reason described in the article is the common causes that you can easily resolve yourself. Low or dead batteries, incompatible batteries, or other underlying factors can contribute to this problem. 

Also, you can follow proper maintenance practices, and use compatible batteries. Also, professional assistance can ensure the mower performs optimally.

5 thoughts on “Dewalt Lawn Mower Flashing Red Light: Solved!”

  1. Pingback: How To Remove Milwaukee Battery M12: 5 Quick Steps

  2. Pingback: Dewalt Flexvolt Compressor Won’t Turn On: Reasons & Solutions

  3. Red light comes on when I engage the start lever. I bought two 9an flexvolt batteries new. Charged my 2×20 still does the same thing. Batteries are good I tried them in my chain saw pole saw weed eastern and hedger. They all ran fine. All my battery tools are dewalt. I’ve checked the contacts checked the blade turns free. I want to stay with dewalt I’ve got all my tools on my service truck dewalt. 1000.00s of dollars invested. Please help me with this. Thanks

  4. Pingback: Dewalt Charger Solid Red Light But Not Charging: Troubleshooting Guide!

Leave a Comment

Your email address will not be published. Required fields are marked *

Scroll to Top