Why Does My Riding Lawn Mower Battery Keep Dying?

Electrical problems are sometimes difficult to isolate and repair.  If your riding lawn mower battery keeps dying, that’s a surefire way to know that something is wrong.  But how do we go about fixing it?

Tools Needed (Commissions Earned)

Diagnosis

If every time you go to start your riding lawn mower you find that the battery is dead, that’s a good indication that something is wrong.

The challenging part comes from trying to isolate the culprit.  Let’s start with the easiest solutions and work our way up.

Start With the battery

Most commonly, you’ll find that the battery itself is past its prime.  Most riding lawn mower batteries have a lifespan of 3-4 years.  Check the manufacture date on the battery to see how old it is.  If it’s nearing that 3-4 years, consider getting a new one.  Even though it might take a charge, the battery might dissipate enough while in storage to be left dead the next time you go to start it.

Inspect the battery posts and cables to make sure that they’re clean and free of corrosion.  Then, make sure the connections are tight.

Make sure the battery is fully charged.  Ideally, you would put a battery charger on it to ensure that it’s full.  If you don’t have that option, you can use a portable jumper pack to supply additional power to start the engine.  Once it’s running, the charging system will charge the battery if left running.

That is, if it’s working correctly.

Alternator and Voltage Regulator

With a multimeter set to DC voltage, place the leads on the battery terminals when the machine is running.  You should see the voltage somewhere between 13-14 volts.  If it’s less than that, then the alternator is not working correctly and should be replaced.

If it’s above 14 volts, then the voltage regulator is going bad and should be replaced.

Another way to confirm if the alternator is bad is to turn your lights on and then shut off the machine.  The lights should dim if the alternator is working correctly.  If they stay bright, then that’s another sign that the alternator is bad.

In order for the charging system to function properly, the machine needs to be running full throttle.  It’s fine to let it idle if you’re just sitting, but if you’re doing any work with your machine it should be run wide open.  When the throttle is not full, the charging system cannot deliver the adequate voltage to the battery.

Parasitic Draws

WIth older machines, this isn’t very common.  Newer riding lawn mowers = more electronics.  Every electrical component increases the potential for a parasitic draw.

With your multimeter in the ammeter mode and the machine completely off, attach the leads to the battery posts.  If you get a reading above 1mA, then that means that something is draining the battery.

Unfortunately, this is where the real detective work comes in.

You’ll have to ensure that every electrical component is actually turned off and try to isolate each one in order to find the culprit.

A wiring schematic can really be your friend to try and isolate different electrical paths.  Just take them one by one to find out which one is causing the drain.

Recap

If your riding lawn mower battery keeps dying, the problem is usually the battery itself.  Check the manufacturer’s date and clean the terminals.  Ensure that the connections are tight.  Make sure it’s fully charged and then test the alternator and voltage regulator.  

If these don’t provide the answer, then you’ll have to move on to the more time-consuming task of checking for parasitic draws.

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