Lawn mower battery keeps dying: Common Causes & How to Fix
1Lawn Mower Battery
Most Common Solution
Repair Instructions:
If your lawn mower battery won't start the engine, one or more battery cells could be dead. Try fully recharging the battery with a charger to revive it. If it still fails to hold a charge, the battery likely needs replacement. Over time, batteries deteriorate and lose their ability to store energy. Telltale signs like slow cranking, dim lights, and quick discharge after mowing indicate a weak battery. Extreme temperatures, improper storage, and infrequent use can accelerate battery demise. When replacing the battery, match the mower's voltage and cold cranking amps specifications.
How to Replace Lawn Mower Battery
- Disconnect spark plug wire - Locate the spark plug wire and detach it from the spark plug to prevent accidental starting.
- Remove battery cover - Use a screwdriver to take off the plastic cover protecting the mower battery.
- Disconnect terminals - Remove the negative (-) black cable first, then the positive (+) red cable from battery posts.
- Remove old battery - Take out any retaining brackets or straps holding the old battery in place. Lift it free of mower.
- Install new battery - Set replacement battery into battery tray in same orientation as old one. Secure with original straps.
- Attach battery cables - Connect positive (+) cable to positive (+) battery post first. Then connect negative (-) cable to negative (-) post.
- Replace protective cover - Reinstall the plastic cover over the new battery, taking care not to pinch any cables.
- Reconnect spark plug wire - Reattach the spark plug wire once the new battery is fully installed.
- Start engine - Turn key to start mower engine and confirm proper power from the new battery before fully reassembling mower.
2Lawn Mower Charger
Most Common Solution
Repair Instructions:
If your lawn mower battery charger is not working, it may have an issue. Use a multimeter to check the charger's voltage output. It should match the charger's rated voltage, like 12 or 24 volts. Low or inconsistent voltage readings indicate a faulty charger needing replacement. Also test the electrical outlet powering the charger. Use the multimeter to verify 120 volt power to the outlet. Flip any tripped breakers feeding the outlet as well. Problematic outlets with low voltage, frequent trips, or improper wiring can prevent proper battery charging.
How to Replace Lawn Mower Battery Charger
- Disconnect spark plug wire - Locate the spark plug wire and detach it from the spark plug to prevent accidental starting.
- Unplug charger - Unplug the AC power cord from the electrical outlet as well as the charging cables from the mower battery.
- Remove charger - Use a wrench or screwdriver to detach any mounting brackets or hardware securing the old charger unit.
- Install new charger - Place the replacement charger in the same location and use original hardware to mount it securely.
- Connect charging cables - Attach the positive (+) and negative (-) charging cables to the corresponding battery terminals.
- Plug in AC power - Insert the new charger's AC power cord into a protected electrical outlet. Make sure wires are safely routed.
- Connect monitoring - As applicable, attach any monitoring wires between the charger and mower control module to enable charge status display.
- Reconnect spark plug - Reattach the spark plug wire once the new charger is fully installed.
- Test operation - Turn on the charger to confirm proper battery charging functionality before using the mower.
- Charge battery - Fully charge the mower battery prior to first use to ensure optimum performance.
3Lawn Mower Alternator
Most Common Solution
Repair Instructions:
The alternator powers your mower's electrical system and recharges the battery while the engine runs. To test if a faulty alternator is the culprit, use a multimeter to check its voltage output. Consult the mower's wiring diagram to identify the correct test points. Too low of a reading indicates a bad alternator not producing sufficient current. No increase from idle to high revs can mean a malfunctioning voltage regulator. Replace the whole alternator assembly if defective.
How to Replace Lawn Mower Alternator
- Disconnect spark plug wire - Locate the spark plug wire and detach it from the spark plug to prevent accidental starting.
- Disconnect wires - Remove wires from alternator terminals, labeling each for proper reconnection.
- Loosen belt tension - Use pry bar to relieve tension on alternator belt and slip it off the pulley.
- Remove alternator - Take out mounting bolts to detach the old alternator from the engine block.
- Install new alternator - Position replacement alternator against block and hand thread mounting bolts.
- Tighten hardware - Use wrenches to tighten the alternator mounting bolts to the proper torque specification.
- Replace belt - Route the alternator belt over the pulley and apply proper tension.
- Reconnect wires - Referring to labels, attach the electrical leads to the correct terminals on the new alternator.
- Reconnect spark plug - Reattach the spark plug wire once the new alternator is fully installed.
- Test operation - Start the mower engine to confirm proper voltage output from the replaced alternator.
4Lawn Mower Voltage Regulator
Common Solution
Repair Instructions:
The voltage regulator controls power flow from the alternator to the battery. It ensures the battery receives the proper charging voltage while the mower runs. If the regulator malfunctions, the battery may not fully charge. This can quickly drain the battery and cause start-up issues. To test the regulator, check the alternator voltage with the engine off and at high idle. Also watch for battery drain within a few hours of running the mower. That's another sign of inadequate charging. Replace the voltage regulator or the whole alternator assembly if faulty.
How to Replace Lawn Mower Voltage Regulator
- Disconnect the spark plug wire - Locate the spark plug wire and detach it from the spark plug to prevent accidental starting.
- Disconnect wires - Remove the wires from the old voltage regulator terminals. Label wires to ensure proper reconnection.
- Remove regulator - Take out any mounting screws or nuts and detach the old voltage regulator unit.
- Install new regulator - Position the replacement regulator in the same location and secure using the original hardware.
- Reconnect wires - Following earlier labels, push the wires onto the corresponding terminals on the new voltage regulator.
- Check connections - Confirm wires are securely attached and properly routed with no risk of touching hot or moving parts.
- Reconnect spark plug - Reattach the spark plug wire once the new regulator is installed.
- Test operation - Start the mower engine to verify proper voltage control from the replaced regulator.
- Make adjustments - If issues, check wiring connections and make any necessary adjustments to regulator mounting or wire routing.