Why Does My Lawn Mower Battery Keep Dying?

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The lawn-cutting season has just gotten underway, but you’ve discovered the battery which assists in getting your gas-powered walk-behind lawn mower or riding mower running is not holding enough of a charge to turn over the engine. Why does your lawn mower battery keep dying? Repair Clinic has done the research and this article will provide some answers, starting with what a battery’s purpose is on a gas-powered lawn mower.

The purpose of a gas-powered lawn mower battery

While most gasoline-fueled lawn mowers utilize a four-cycle engine to power the equipment, riding mowers and electric start walk-behind mowers will also use a battery to turn over the engine as well as supply power to other components like an electric clutch and headlights.

The lawn mower battery converts chemical energy into electrical energy to start the engine

Similar to how a car engine is started, when the mower’s ignition key is turned or the start button is pressed, chemicals within the battery begin to react to convert chemical energy into the electrical energy needed to start the engine. Once the engine is running, the spinning magnets on the engine’s flywheel, or an alternator, will recharge the battery so it will be ready to restart the engine for the next mowing session.

What type of batteries are used on lawn mowers?

Most riding mower batteries will contain lead acid which allows for recharging, although some mowers will also rely on lithium-ion or lithium-iron-phosphate batteries. For lead acid batteries, lead is submerged into sulfuric acid where the sulfates from the acid will adhere to the lead, a chemical reaction which produces the electricity needed to start the mower engine and power the lights and other components. The spinning flywheel magnets or alternator will reverse this chemical reaction by causing the sulfates to return to the acid, recharging the battery.

Lithium-ion batteries are the popular choice for walk behind lawn mowers

As the name implies, a lithium-iron-phosphate battery will use iron phosphate for the chemical reaction to produce electricity; a lithium-ion battery will use various forms of oxide (cobalt, manganese, nickel) to accomplish the same thing. While both are rechargeable, lithium-ion batteries have a higher energy density which allows the batteries to be smaller. This makes them a more popular choice to use on walk-behind lawn mowers.

The 4 potential causes of a lawn mower battery that keeps dying

If your lawn mower battery won’t hold a charge, here are the four potential causes you should troubleshoot:

  1. Faulty battery – It’s the most obvious cause, but one or more cells in the battery itself may be dead. If your battery is used on a walk-behind mower, you should try charging the battery using a dedicated battery charger. If the battery still won’t hold a charge, the battery is likely faulty and should be replaced with a new one.
  2. Malfunctioning charger  – The charger you’re using to recharge the battery could be malfunctioning and unable to provide a full charge as well. You can use a multimeter to test the charger to determine if it’s providing the proper voltage output. You should also use the multimeter to test the electrical outlet the charger is plugged into to make sure the outlet is providing sufficient voltage. Keep in mind, if the electrical outlet isn’t providing any voltage, you should check to see if the circuit breaker for that particular outlet circuit has tripped. While this may seem obvious, it’s a troubleshooting step that is easy to overlook.
  3. Defective alternator – Riding mowers will use an alternator to provide voltage to the mower while the engine is running and it will also recharge the battery. A defective alternator may not be able to recharge the battery, weakening the component. To help determine if the alternator is defective, you can use a multimeter to test the alternator’s voltage output according to the component’s wiring diagram.
  4. Defective voltage regulator – The voltage regulator allows the proper amount of voltage to be sent from the alternator to the riding mower’s battery. A defective regulator can prevent the battery from receiving enough voltage, causing the battery to drain quickly. As with the alternator, you can use a multimeter to test the regulator by referring to the component’s wiring diagram. If the regulator tests poorly, you can replace the part with a new one to solve the problem.
Gas-Powered Lawn Mower Battery Keeps Dying?

Repair Clinic provides free do-it-yourself repair help

As your repair partner, Repair Clinic provides free do-it-yourself repair help via the “Videos & Articles” section of its website. Enter the full model number of your lawn mower or the mower’s engine in the search bar to discover all the relevant “how to” videos, step-by-step guides, diagrams, and schematics on hand to assist with your repair. Want to know how to install a new alternator on a Briggs & Stratton engine (Model 331977-0010-G1)? Repair Clinic has a video to show you how. Need a primer on how to use a multimeter to measure the voltage at an electrical outlet? There’s a video to guide you through that process as well.

The lawn mower parts you need are only a click away at Repair Clinic

In addition to providing you with unparalleled repair help, Repair Clinic stocks the parts you need to fix your lawn mower or the mower’s engine, genuine manufacturer parts from such top industry names as Briggs & Stratton, Craftsman, Honda, Husqvarna, MTD, Murray, Snapper, Troy-bilt, and Toro. Repair Clinic also makes it easy to find the exact genuine OEM part you need: simply enter the full model number of the lawn mower or the mower’s engine in the Repair Clinic search bar to see a complete list of all compatible parts. You can then use the “Part Category” filter (example: “Alternator, Battery & Charger”) followed by the “Part Title” filter (example: “Voltage Regulator”) to refine that list to locate the specific replacement part you’re looking for.

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