Only a few days ago you charged your mower battery and took it for a spin. You hauled mulch around to the flower beds and zoomed around getting your landscaping done. All was right with your mower. Fast forward a few days, the grass needs cutting but the battery needs to charge again? What’s going on? The same thing happened the last time you used it, and you get a repeat this week. You ask yourself “why is my mower battery draining?”
We will be going over possible issues that could be draining your lawn mower battery, how to fix them, and if a bad solenoid will drain a lawn mower battery. Get comfortable, crack open a cold one, and let’s start solving the problem.
What Keeps Draining My Lawn Mower Battery? (The Short Answer)
Your lawn mower battery could be draining from a number of causes such as loose, dirty, or corroded battery cables, electronic drain, or a bad battery. There could also be a faulty charging system, a failing voltage regulator, or other issues that are draining your lawn mower battery.
Possible Reasons for a Lawn Mower Battery Not Holding a Charge
- Dirty or corroded battery cables
- Loose battery cables
- Leaving the key on in the ignition or leaving lights and accessories on
- Bad alternator
- The voltage regulator is going bad
- The battery needs maintenance
- Not running your mower at full throttle
- The battery is failing
- Electronic drain
Dirty or Corroded Battery Cables
It happens to your automobiles, and it can certainly happen to your lawn mower battery. You open up the hood, there on the battery cables is a whitish, powdery crust building up around the terminals.
Hydrogen gas escapes from your battery and it reacts with the metal on the battery posts and cables causing corrosion. If it gets too bad, your lawn mower battery will not charge or send power to the mower at all. It’s annoying, but a simple fix.
How to Fix: Put on your safety gear, chemical-resistant gloves, eye protection, all that stuff. There could be some battery acid, or the corrosion could be irritating to skin and mess up clothing.
Disconnect the battery terminals, pour baking soda (you can also use battery cleaner from your local auto parts store) around the corroded areas, and then pour a little bit of water on the baking soda to neutralize the corrosion and battery acid.
If the corrosion is stuck on, you can use a small wire brush to scrape it off, then use more baking soda and water to dissolve the residual corrosion. Use paper towels next to clean and dry the areas then reattach the cables, charge your battery again, and you’re good to ‘mow’.
Loose Battery Cables
If you have a loose connection, then of course the battery is going to struggle to keep everything running correctly. The constant vibrations of the motor over time can cause the bolts to loosen slightly causing your battery to work overtime to power your lawn mower.
How to Fix: Simply wiggle all the cable connections to see if they are loose. If any need tightening, clamp them down properly then get back to tending your yard.
Leaving the Key on in the Ignition, or Leaving Accessories on
This could happen. I’m forgetful at the best of times, and even more so when I’m in a hurry. I get it, things happen, maybe the key wasn’t turned completely off, or the lights were on in the daytime, and you just didn’t see that they’d been left on. We’re all very busy people and simple mistakes like this do happen.
How to Fix: To fix this problem simply double-check yourself. Take the keys out and hang them somewhere nearby or put them in the cupholder of your mower. After you park it, take a quick look to make sure all the lights and fancy gadgets are turned off.
A Bad Alternator
The alternator helps to keep the electrical system running and recharges the battery while the engine is running. If the alternator is failing, then it means the battery has to take up the slack and it’s not getting enough charge to keep it in tip-top shape.
How to Check: To check the alternator, turn the mower’s lights on, leave them on then turn off the mower. If the alternator is good, then the lights will dim when the motor stops. If the lights remain the same intensity, then it means the battery is carrying the load and the alternator needs to be replaced. Once that is fixed, the battery will be recharged every time you run your mower.
The Voltage Regulator is Going Bad
If the voltage regulator is going bad you’ll notice some obvious symptoms, namely that it will cause the battery to drain pretty quickly.
How to Check: You will need your trusty multimeter to check for this problem. Set it to check the voltage, turn on the mower just enough to get a load running through the electrical system. Check the battery terminals with the multimeter.
You are looking for voltage between 13.8 and 14.5 volts. Below 13.8 means your battery is failing or is not sufficiently charged, and above 14.5 means you have a fault in the voltage regulator, and it needs to be replaced.
The Battery Needs Maintenance
Another reason your battery is not able to keep a charge is that your battery needs some maintenance. Lawn mower and car batteries are known as wet cell batteries. There is sulfuric acid inside the battery cells and over time gasses escape, the liquid is reduced, resulting in a poor performing battery. Learning how to restore a lawn mower battery can save you a few bucks when this happens.
How to Fix: You can check this by first donning your protective gear. Gloves, safety glasses, you know the drill.
Next, carefully pop off the plastic covers to the battery and peer inside. If the liquid is lower than the round ports, it needs water. Use a small funnel and pour distilled water into the ports to raise the liquid level only to the bottom of the ports. You don’t want to overfill these holes. Put the covers back when you’re done, give the battery a good charge and you should be set.
Now is also a good time to check for dirt and corrosion at the battery terminals.
Not Running Your Mower at Full Throttle
Now I’ve been guilty of this in the past. I was young, just bought my first John Deere riding mower and I wanted to eventually pass it on to my grandchildren. In an effort to reduce the strain on the mower, I didn’t run it at full throttle. Little did I know, mowers are designed to run with the “pedal to the metal.”
Along with other issues that can occur from not pushing the throttle to the top, it can drain your battery. If the motor is not running at full RPMs, the battery may not be getting a full charge. So go ahead, crank that throttle up and run your mower full blast. It was built to run full throttle.
Your Battery is Failing
Another reason your lawn mower battery keeps draining could be because it is heading toward the end of its life cycle. Mower batteries typically have a lifespan between 3 to 5 years with proper care.
Of course, you can get the occasional lemon that doesn’t even tick on that long, but if you can’t find anything else that keeps draining your battery, you might have to think about replacing your old one. When you’ve got a battery that’s soon to be a dead lawn mower battery, the simple fix is to buy another one. I know your wallet isn’t going to be excited about that, but once the battery starts failing, there’s nothing else that can be done about it.
With all the new advances related to everything electronic, your battery could be experiencing a parasitic electronic drain. This happens when the lawn mower is turned off, but a tiny electrical charge is still sucking minute doses of power.
Given time, this could weaken or completely drain the battery. This can be difficult to check for and to fix, but if all other avenues have been exhausted, you may have to check for this. You will need a multimeter for this particular diagnosis.
How to Check: Set your multimeter to ammeter mode then set the probes on the battery posts when the mower is turned completely off. If you get a reading of more than 1mA, then your electrical system is still drawing current off the battery via a relay system, or a component in the mower that has a standby mode.
To remedy the parasitic drain, you may have to take it in to get your mower serviced. You could also disconnect the battery each time to save it from the power-sucking culprit or keep a maintenance charger on the battery when not in use.
Will a Bad Solenoid Drain the Battery on a Lawn Mower?
The solenoid is the part connected between the battery cable and the starter. A bad solenoid will not drain the battery on a lawn mower – its main purpose is to send a larger charge to the starter to get the mower running. If the solenoid has gone bad, assuming the battery is still good, you will probably only hear a small click when you attempt to start your mower.
I hope this has answered all your questions as to what keeps draining your lawn mower battery. Now you don’t have to continue asking yourself or your neighbors why your John Deere tractor or your Kohler engine keeps draining the battery. You have the knowledge to diagnose and fix the draining battery yourself.
By checking the battery cables for corrosion or a loose fit, keeping up with battery maintenance, and making sure everything is turned off (yes, I’m speaking to myself here) as well as checking for alternator, voltage regulator problems, or electrical parasites you can find out what keeps draining your mower battery. Also, replace the battery if it has reached the end of its life cycle, and keep that throttle running high, so you can keep that battery charged, and your lawn neat and tidy.