Lawnmower Battery Dying: Causes

Most lawnmowers have a 12-volt battery, although there are smaller ones with a 6-volt battery. Regardless of the size, the battery in a riding lawn mower is what produces the power to crank the engine. Once the engine starts to run, the mower’s recharging system keeps powering the battery, and this ensures that it will be able to crank the engine again. If your lawnmower won’t start, it only means that your battery didn’t recharge and is fully drained.

There are several reasons why your lawn mower battery keeps dying. They include:


Bad Battery

A lawn mower’s battery is expected to work perfectly for a period of four years, after which its holding capacity starts to decline. This could be due to damage of one or more cells in the battery that ends up affecting the charging process. Since a lawnmower has a small storage capacity, even the smallest reduction in the amount of power could affect its effectiveness.

A lawnmower will not run with a bad battery.  Or, at least it won’t start.  Once the mower is started, it should get enough power to run from the stator or alternator.

Try charging the battery up with a battery charger, and if unsuccessful, it means that the battery is defective and should be replaced.


Battery Not Charging

Mower Battery Keeps Dying Fix

It’s vital to understand the battery recharging system to help deal with battery issues. The alternator and voltage regulator is responsible for charging the battery, and if any of these parts fail, your mower will not perform effectively. Running your mower while not at full power will lower the effectiveness of the battery’s charging system. Running it at full throttle, on the other hand, will give it the correct number of revolutions per minute to recharge the battery.

Loose connections on the battery can also make it work harder, thereby draining off its power more quickly than usual. Tightening these loose connections should be able to renew the battery’s ability to hold a charge.


Corroded Battery

Corrosion happens when there is a reaction of hydrogen gas released from the acid and other particles present in the air. It can also be caused by current flowing during the charging/discharging process. In this case, corrosion will occur if there was a current draw on the battery even when the lawnmower wasn’t in use. If the terminals of the battery are corroded, then the battery’s power will not be delivered properly.

To avoid this, you should use a solenoid on the carb to help shut off the fuel when the ignition is switched off. Cleaning the posts with a wire brush and baking soda and later applying petroleum jelly to the terminals will also prevent further corrosion.


Mower’s Components Still On

A parasitic drain may occur when certain components that are supposed to shut off, such as the electrical relay, are still running while the engine is shut off. At times, you may switch off the mower but forget the headlamps on or even leave the key on in the switch. This mistake will drain the battery since power is still supplied to the electrical components, although the engine is off.

Always ensure that the headlight is off, then turn off your mower, and later switch the key off. It would be best if you disconnected the battery cables when through with the mowing before putting it in your storage.

One way to check if your mower has this condition is to test for the current draw when the engine is still turned off. Disconnect your positive battery cable and connect an ammeter between the battery cable and the positive battery terminal. If the ammeter shows current draw of more than one milliamp, it means that the electrical system is drawing power though the engine is off.

See Also:  Lawn Mower Not Starting Guide


Bottom Line

If your battery is always draining, you can slow charge it before using it again to boost its charging system and prevent frequent dying. However, if the problem persists and keeps falling out of hand, it’s important that you call in a qualified technician to assess your lawn mower battery.