The lawn mowersmall engine often has a separate model number. Use the small engine model number for a complete list of symptoms and parts. Watch our model # lookup video for help finding the model number.
The part(s) or condition(s) listed below for the symptom Lawn mower battery keeps dying are ordered from most likely to least likely to occur. Check or test each item, starting with the items at the top of the page.
The alternator provides power to the lawn mower while the engine is running and recharges the battery when the engine is not running. If the lawn mower has headlights, turn on the headlights and then turn off the engine while watching the headlights. If the lights dim when you turn off the engine, the alternator is working properly. If the lights do not dim, the alternator is likely defective. To determine if the alternator is defective, use a multimeter to test the alternator voltage output according to the wiring diagram.
While the engine is running, the voltage regulator sends the proper amount of voltage from the alternator to the battery to keep the battery charged. If the voltage regulator is defective, the battery won't receive enough voltage, causing the battery to drain quickly.