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10 Reasons a Sun Joe Electric Battery Mower Won’t Start: SOLVED

More homeowners are choosing to use electric mowers because they are quiet and require less maintenance than traditional gas-powered mowers. While this is true, they are not maintenance-free and can still develop starting problems.

A Sun Joe electric battery mower may not start due to an insufficient power supply, bad electrical connection, overworking the motor, or an incorrect operating procedure.

This may be caused by a bad battery connection, a dead or bad battery, a faulty safety switch, loose wires or damaged wires, or a buildup of debris under the mower deck.

Before performing repairs on your cordless Sun Joe mower, take all safety precautions when working with electric currents and sharp blades. Remove the safety button (key) and battery.

If your mower is still covered under Sun Joe’s warranty period, consult with Sun Joe before performing repairs so you don’t void that warranty.

Battery mower won't start

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Follow all safety instructions provided in your equipment operator’s manual before diagnosing, repairing, or operating. Consult a professional if you don’t have the skills, or knowledge or are not in the condition to perform the repair safely.

Reasons For a Starting Problem on a Sun Joe Electric Mower

1. Insufficient Battery Power

Of course, a battery-powered mower won’t start when it isn’t getting good power from the battery. Many items can cause insufficient power including bad battery connections, incorrect battery installation, and a failing battery.

Check to make sure you are using a battery that is compatible with your electric mower. Using the wrong size battery may cause a failure to start condition in addition to more severe problems with the electrical system.

2. Battery is Not Correctly Installed

Check the installation of your battery in the battery port. Make sure it is securely in place and making good contact.

Wipe off the lid of the battery compartment before opening it to keep dirt and debris from falling into the compartment.

For Sun Joe mowers with an external battery that is installed, the battery should slide into the guide rails and snap into place. The lid must be able to securely close.

3. Bad Connection with the Charger or Wall Outlet

Sun Joe offers electric mowers with batteries that have to be removed and placed on an external charging system and mowers with internal batteries that are charged while installed in the mower.

Whatever type of charging system you have on your mower, always use a charger or charger cord that is designed specifically for the battery you are charging.

Check the outlet to ensure the battery charger is fully plugged in. Use a standard 120V household outlet. Make sure there is sufficient power at the outlet.

The plug style on your Sun Joe cord must match the style of your outlet. Do not attempt to modify the plug. A three-prog style plug must be inserted into the same 3-prog style outlet.

Replace a damaged charger or charging cord.

4. Battery is Excessively Hot

A hot Sun Joe battery will cause your mower to shut down and not start. Clean the vents on your mower. Let your battery cool before attempting to start again.

Clean the vents and keep the battery charger out of areas of extreme heat or cold.

5. Battery Is Dead

Sun Joe lawn mowers rely on a battery for power so it’s no surprise the mower won’t start when the battery is dead.

  • Sun Joe mowers with an external battery charger require the battery to be removed to charge.
  • Sun Joe mower with an internal battery requires a charging cord to charge the battery while installed on the mower.

Charge the battery until it is fully charged. Once fully charged, unplug the charger. This is to avoid damage because the charger does not automatically shut off once the battery is fully charged.

LED Lighting System

Most chargers utilize an LED lighting system to indicate the battery charging status. I have listed a description of the lighting system for many Sun Joe battery chargers.

Refer to your charger manual for a description of the light indicators specific to your charger model.

  • Red light: The battery is charging.
  • Green light: The battery is charged.

Indications a Battery is Going Bad

Batteries begin to fail when they become old, are exposed to extreme temperatures, or fail mechanically. Here are a few things to watch for that may indicate your battery is going bad and you need to purchase a new one:

  • The battery doesn’t hold a charge as long as it once did.
  • The battery gets very hot.
  • The battery is charging slowly.

6. Incorrect Starting Procedure

Whenever you get a new battery lawn mower or one that is just new to you, make sure you check its operator’s manual to learn about the safety features and recommendations on your Sun Joe mower.

Sun Joe’s safety key is a safety mechanism meant to prevent children from accidentally depressing the safety handle and starting your mower. Not following this starting procedure will prevent your mower from starting.

Push Mower and Self-Propelled Mower Starting Procedure:

  • Ensure the battery is securely in place.
  • Insert the safety key into the battery compartment and close the cover.
  • Press the safety lock button and pull the switch lever toward the handle or squeeze one of the on/off switches on the handle (depending on your model) to start the motor.
  • Release the release safety lock button.
  • The mower will shut off when you release the switch lever or no longer squeeze one of the on/off switches.

7. Bad Safety Switch

If any of your safety switches fail, your mower may fail to start. You can test each switch with a multimeter or by temporarily bypassing them with a jumper wire.

Replace any bad switch. For your safety and the safety of others, never operate your mower without all of the safety switches in working order.

Check out my article on the dangers of electric mowers so you understand why you need to take caution when working on and operating your electric mower.

8. Loose or Pinched Wires

You will have many electrical wires running through your Sun Joe mower and along the handle. A wire may develop a short when a wire becomes loose or pinched.

Sometimes wiggling a wire will identify a short preventing the mower from starting. You can also use a multimeter to identify a short.

A common area for a pinched wire is near the handle where some handles fold for storage. To avoid pinching wires in this area, be careful folding and unfolding the handle.

If you do find a pinched wire, you can repair it using a wire nut. Before beginning the repair, remove the battery and the safety button.

You may want to contact Sun Joe before making the repair if your mower is still covered under warranty.

Repairs to the wiring and any modifications to the mower can void all warranties offered by Sun Joe when performed outside of an authorized Sun Joe repair center.

9. Debris is Restricting Blade Rotation

It is not uncommon for excess grass and other debris to get lodged or stuck under your Sun Joe lawn mower’s deck.

Again, always remove the battery and safety key before performing any maintenance on the deck.

Large amounts of grass in the electric lawn mower deck might be inhibiting your blade’s ability to rotate which can be the root cause of the lawn mower refusing to start.

Your Sun Joe mower may also stop mowing and not start when the mower is overloaded. This can happen when you are attempting to cut too much grass at once due to it being thick, tall, or wet.

When you are having this problem, you will need to raise the mower cutting height and slow down your speed so the load is decreased on your Sun Joe mower. Avoid cutting wet grass.

10. Damaged Components

If you reached this section and still haven’t found the problem with your mower, you should have an authorized Sun Joe service center look at the mower.

You may have damaged the motor or other parts on your mower that will need to be replaced.

A trained service technician will be able to perform tests to determine the cause of your starting problem. You can get support from Sun Joe by calling 1-866-766-9563.

Don’t Operate a Sun Joe Electric Mower in the Rain

Water can cause your lawn mower to short out and not start. Read more about the effects of using your electric mower in the rain in Can You Use an Electric Mower in the Rain?