“What keeps draining my lawn mower battery?” is a question most gardeners have asked in frustration, even when they regularly charge it on time. We understand how frustrating it is to see the battery charging percentage decrease faster than it should.

What Keeps Draining My Lawn Mower Battery

The battery might be draining for several reasons such as poor maintenance, faulty cables, an old charger type, or a defective voltage regulator.

Find out why the mower battery might not hold the charge as needed, along with the easiest possible solutions here.

What Factors Keep Draining Your Lawn Mower Battery?

The factors that keep draining your lawn mower battery include damaged, loose, or corroded cables, an electronic drain, or cables that are attached loosely. Sometimes, it is as simple as the battery needing some maintenance. Other plausible reasons are faulty alternators, voltage regulators, and battery chargers.

– Cables Attached Loosely

Sometimes, the battery seems to be draining fast by something as simple as loose cables. Mostly, mower batteries are connected to the engine through two main cables. The black one attaches to the negative terminal, while the red one goes with the battery’s positive terminal. 

Gain access to your battery first to check if the cables are attached properly. The battery is usually placed in a deck near the handle in push-type mowers. In riding lawnmowers, the battery is located under the seating of the mower.

Once you have access to your battery, follow the cables to the solenoid. Make sure they are securely attached on both ends. Before touching the battery to correct loose connections, turn the ignition switch off and take the key out.

– Faulty Battery Cables

How long has it been since you last took out your battery for inspection and maintenance? The terminals of battery cables often get corroded, draining the battery like nothing else. Turn off the engine, gain access to the battery and check these terminals for yourself.

During the checkup, follow the cables from one end to another to see if they are damaged or corrupted anywhere. In most cases, the terminals get corroded from leaking blue-green fluids. If the positive or the negative cables have been damaged, they might need to be removed.

Faulty Battery Cables

Take the battery out first, making 100 percent sure that the mower engine is turned off. Always remove the negative terminal first to break the circuit, followed by removing the positive terminal. Once the battery is out, you can replace faulty cables with new ones or eliminate corrosion. 

A baking soda solution is an effective homemade remedy to eliminate corrosion and clean the battery. Add five or six full teaspoons of baking soda in four cups of distilled water and then use this paste to get rid of the corrosion products formed on the battery terminals.

– Battery Needs Maintenance

A lawn mower battery requires regular maintenance just as much as your car, albeit less frequently. Most of the time, the batteries in our mowers are lead-acid, with sulfuric acid as the electrolyte. While using the mower, the battery gets heated and gasses are produced, which eventually decrease the charge-holding capacity of the battery.

The good news is that maintaining a healthy battery is quite straightforward. In a few simple steps carried out carefully, you can easily restore a battery to its former glory. 

  1. The mower battery needs to be taken out of its case for proper maintenance. Before you do that, ensure you have worn thick rubber gloves, goggles over the eyes, and full-sleeved clothes.
  2. Unscrew the locks keeping the battery in its place within the mower, disconnecting the negative terminal and then the positive terminal. 
  3. Carefully lift the battery and place it on a flat, clean surface. Inspect the battery cells and check the level of fluid present within each. If fluid levels are lower, use distilled water to raise them to the required levels.
  4. Sometimes, it’s best to drain the old fluid from each cell and refill it with a brand-new solution. Be careful not to give yourself a burn when removing the lids from the cells and draining the electrolyte into an appropriate container.
  5. Clean the battery cells using a DIY baking soda and distilled water cleaning solution. For removing corrosion products, you can use sandpaper with 300 to 400 grit. 
  6. Make your battery fluid using a saturated Epsom salt and distilled water solution. Use a dropper or a funnel to pour this fluid into each newly cleaned cell.
  7. Before placing the battery back in its place, charge it for 24 hours at a rate of two amperes per hour. You will see how improved your battery’s performance becomes after each maintenance session.


– Accidentally Leaving the Engine Running

The lawnmower battery might not be holding a charge for the appropriate amount of time when the engine is not turned off properly. This often happens with mowers that turn on and off using a key. The key to these mowers needs to be turned all the way through and then preferably taken out.

The same goes when you must remember to turn off the lights and leave the engine partially running. This is common even with mowers that turn on and off using buttons. Don’t worry; nobody will judge you for sometimes being forgetful with the mower. 

Just be aware that doing this often can cost you the battery life of your precious lawn mower. Whenever you are done cutting grass, always double-check to see that all the lights are off and that the engine is also completely off with the key taken out. 

– Alternator Gone Bad

The alternator is an important engine system that keeps the battery charged while the engine is running. If the alternator becomes faulty and damaged, the battery loses charge faster than normal. Lucky for you, it is quite simple to check the condition of a mower’s alternator.

Here is how to check the alternator. Start your mower and turn its lights on, then leaving the lights on, turn the mower’s engine off.

Alternator Gone Bad

If the lights dim once the engine stops, your alternator is in good shape. However, the alternator must be replaced if the light intensity stays the same even after the engine is turned off.

In this case, the battery bears most of the load while not being recharged during work. This constant draining could potentially and permanently damage the battery. It would be best to call in your mechanic and have them replace the alternator right away. 

– Faulty Voltage Regulator

When the voltage regulator of the battery stops working, it starts draining charge faster than ever. The voltage regulator’s job is to keep the voltage of the battery constant regardless of fluctuating inputs and outputs. 

Most modern lawnmowers keep their battery voltage regulated to 12, while some older designs still run on a six-volt battery. Before you take your mower engine to the mechanic for repair, here is how to ensure the problem lies within the voltage regulator. 

  1. You will need a multimeter to check whether the voltage regulator is working properly. Set it in voltage reading mode and ignite the lawnmower’s engine.
  2. Turn the ignition key partially, so the lights are on before connecting the multimeter to the battery.
  3. The positive terminal of the multimeter is to be attached to the battery’s positive terminal. 
  4. Next, attach the multimeter’s negative terminal to the battery’s negative terminal. 
  5. The reading on the multimeter’s screen should read somewhere between 13.8 to 14.5 volts in the case of a standard 12 volts battery. Your voltage regulator must be fixed if the readings are out of this range.

– Mower Is Not Run at Full Throttle

How many of us think riding lawnmowers lower than full throttle is good for our mowers? Many people are guilty of thinking this, even though it is completely wrong. Mowers are designed to be used at full throttle, and not doing so starts draining the battery.

The battery must recharge properly when the motor is not rotating at its prescribed RPM, so do not hesitate to put your foot down and use the mower at its full potential. This is what this machine was built for and how it functions properly. It would also make your job so much easier because the mower will now be able to cut grass faster and quicker

– Incorrect Charger

When the charger of your electronic lawn tractor mower is faulty, it will not be able to charge the battery fully. It will begin doing the opposite and draining the battery instead. 

This happens mostly when the charger is of the old type that is not automatic or is without a voltage regulator. If you are not cautious with this type of charger, you will end up overcharging the battery of each type. When the battery is overcharged again and again, it will lose its ability to hold a charge and will begin to drain faster than ever. 

Incorrect Charger

Fortunately, this is the one condition with the easiest fix. Throw away this old charger and buy a new one. Only this time, the new charger needs to be automatic so that as soon as the battery is recharged, it shuts down automatically. 

The charger needs to have the option of being put on slow trickle charging. Fast chargers are all the rage, but they harm the battery. Your charger needs to be adjusted to slow settings so it can charge the battery in 24 hours. 

– Electronic Drain

Unbeknownst to you, your battery might be suffering from a parasitic electronic drain that keeps eating all of its charges up, so even when you have turned the engine off and parked the mower for the day, some parts of the engine keep draining the battery.

A parasitic electronic drain is notoriously difficult to diagnose and might soon lead to a dead lawnmower battery if not treated on time. If you have exhausted all other possible causes of a draining battery, you must consider this one seriously.

One way to test for a parasitic drain is to set the multimeter to ammeter mode and then connect it to both terminals of the battery. Make sure that the engine is turned off while you do this. The only way to resolve this problem is to take the mower to a mechanic or the manufacturer for complete top-to-bottom fixing.

– Battery Has Gone Bad

If the battery refuses to charge beyond 12 volts even after charging for several hours, it has simply outlived its lifespan. This is inevitable if the battery is several years old and has not been well maintained.

Battery Has Gone Bad

Still, charge this battery with a trickle charger for a day to ensure it is dead. Afterward, turn the ignition key and the spark plug off, and disconnect the cables attached to the battery. The black one is always removed before the red one breaks the circuit properly.

Take the old battery to the store and buy a new one. Most stores will give you a good discount for depositing the old battery even if it is completely dead. You get to save upto $15 to $25, which is a good deal.  


You have finally reached the end of this comprehensive guide on why mower batteries drain so often.

We have discussed a lot of possible reasons on why your mower’s battery keeps draining, so here are some key points you need to remember as we conclude tihs guide.

  • The most common factor that keeps draining your battery is cables that are broken, corrupted, or not attached properly. 
  • In the case of a lead-acid type of battery, you should improve its fluid level by adding distilled water.
  • If the engine’s voltage regulator or the alternator is defective, get it fixed by a professional to keep the battery charged.
  • Not using the mower at full throttle drains the battery’s charge and is not recommended to be done frequently.

Every time you face the problem of a battery draining too rapidly, think back on this list to diagnose the root cause of the problem. We are confident that you will not only be able to figure out the cause, but also fix it in no time!

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