How to restore a lawn mower battery after it starts showing trouble is a common question among avid gardeners. Sometimes, all a mower battery needs are to be taken out, cleaned properly, and recharged fully.

How To Restore a Lawn Mower Battery

In this guide, we will discuss in great detail all the steps needed to fix a battery at home, so why take the battery to a mechanic and spend extra money when you can restore it at home? Let’s find out all the easy steps in the guide below.

How Do You Restore Lawn Mower Batteries?

To restore lawn mower batteries, you must first take them out of the mower and drain their charging fluid. After this, the battery needs to be cleaned and the fluid should be refilled. The battery should then be charged again in order to work properly.

Let us go through all the steps of this restoration in detail below.

1. Get Your Equipment Ready

The most important items on your list need to be personal protective equipment. These include thick rubber gloves, clothing that covers the whole body, and protective eyewear.

If you have yet to buy an automatic, voltage-regulated battery charger, it is high time you spend some money on it. This charger might solely be responsible for damaging the battery in the first place.

Next, you will need a lot of distilled water. We are talking about gallons here. Buy a couple of bags of baking soda and Epsom salt as well. Buy a dropper and a funnel to pour electrolytes into the battery.

2. Remove the Battery From the Mower

Lawn mower batteries are in two common locations, either under the hood or under the driving seats of riding-type mowers. In a riding lawn mower, you will have to pull the seat up to gain access to the battery. If your mower is a bit unique and needs help finding its battery, go through its instructions manual to find out where it is.

Before gaining access to the battery, turn the ignition off and take the key out. It is also better to disengage the spark plug to decrease the risk of accidentally starting the engine. Locate and then remove all latches or straps holding the battery down in its place.

When taking the battery out, start by removing its ground wire first. This is going to be the lone black wire in most cases. Then remove the negative terminal of the battery followed by the positive terminal. The negative terminal is usually the black one with the negative sign, while the positive terminal is the red one with the positive symbol etched on it.

Do not pull the cables off by force; instead, carefully loosen them up. If the intervals and the cables seem stuck, use a flathead screwdriver to loosen the connectors apart. Be careful when taking the battery out, and see if you can get someone to help you.

3. Remove Caps From the Cells

On top of the battery, several cells contain electrolyte fluid within them. You will easily be able to see them once you take the battery out. These cells are covered by caps that need to be removed as the first step.

Remove Caps From the Cells

You will need a flat-headed screwdriver because caps are not so easily loosened. Be careful during this process because it’s easy to spill the corrosive electrolyte out during cap removal. Ensure your skin, especially your hands, is covered by thick rubber gloves and full-sleeved clothing.

Sometimes, the caps do not come loose because of severe corrosion on their metal parts. In that case, you should remove the corrosion first by using a baking soda and water mixture. Apply this mixture to the affected parts and scrub the corrosion using a toothbrush. You will see how easily the cap unscrews after this.

4. Drain the Old Electrolyte Out

After the cell caps have been removed, it is time to remove the old electrolyte. Exercise caution to prevent spillage while you are at it, and better use a dropper and a syringe to stay on the safe side. This fluid is toxic and corrosive to the skin, so ensure you are well-covered and protected.

Collect the drained fluid from the battery in a proper metal or plastic container. You cannot just drop this container of fluid into regular garbage. This is considered hazardous waste, and you need to read up on local laws regarding getting rid of it. Ask your municipal garbage disposal company if they accept waste of this kind.

5. Remove Corrosion From the Battery

Over time, some inevitable sulfate from the electrolytic fluid builds up within battery cells. This build-up plays a huge role in decreasing the life span of mower batteries. Cleaning each cell inside and out is crucial in restoring a problematic battery.

The outside can be easily cleaned using only a wet towel unless proper corrosion exists. Corrosion will most likely be present around the battery terminals. There are two vetted ways to get rid of corrosion build-up fast.

The first method is to buy a corrosion-cleaning solution from the store. Pour a few drops of this solution on a paper towel or sponge, then use it to wipe the corrosion off. A premium-quality solution will remove corrosion without much effort on your part.

The second option is to use sandpaper to scrape the green-colored corrosion products off the battery. The sandpaper grit should be around 300 to 400 to make this task easier for you. Don’t use sandpaper with bare hands, or you will get scratches on both hands.

6. Clean the Battery Thoroughly

A homemade baking soda and distilled water solution is more effective at cleaning the mower battery than any commercial cleaner. If you want to, you can also use commercial cleaners, which are usually expensive and less effective.

Take a clean bucket and fill it with one gallon of pure distilled water. Salt or fresh water is not recommended because it leaves the battery’s salt and mineral residue behind. Using the dropper or the funnel, pour this solution into each cell and put the caps back on.

Clean the Battery Thoroughly

Refrain from filling the cells to the brim; leave some space empty at the top. Shake the battery gently for about one to two minutes. This would help the solution clean the insides of battery cells as thoroughly as needed. Allow an extra one to two minutes before draining the cleaning solution out.

To drain the cleaning solution from the battery, invert it into a plastic tub or container. You should not use this dirty water on plants or grass; instead, responsibly dispose of it according to your local laws.

7. Make Epsom Salt and Distilled Water Electrolyte

The next step is to make your DIY electrolyte using magnesium sulfate and distilled water. Magnesium sulfate is usually sold under its common name, Epsom salt. Using any other water except distilled water is a mistake that will destroy the battery.

Take as much as a gallon of distilled water and add about 15 ounces of Epsom salt. Warm the water a little before adding salt, mixing it thoroughly to create a perfectly saturated solution. You now have a perfectly balanced homemade electrolyte solution for lawn mower batteries.

8. Fill Battery Cells With the Electrolyte

Use a clean dropper to fill each cell with your newly made electrolyte solution. Each cell is marked with a line that indicates how much it needs to be filled. Keep a close eye on this line, so you don’t end up overfilling or underfilling the cells.

Fill Battery Cells With the Electrolyte

The temperature of the electrolyte solution needs to be around 60 to 80 degrees Fahrenheit. If the solution has been kept at colder temperatures, bring it to room temperature before pouring it into the cells. There is no need to heat it; leave it in a temperature-maintained room for an hour or so until it reaches the right temperature.

Once the cells have been filled up to the line drawn, you must put their caps back on. However, don’t screw them up too tightly just now as a precaution against overflow during charging.

9. Charge The Battery Fully

Your charger choice matters a lot when restoring a lawn mower battery. Be bold in investing enough money into buying a good-quality automatic battery charger with a voltage regulator. The charger must also be adjustable to set its charging time according to your liking.

Set the charger to the trickle charge option, which charges your battery slowly. At the rate of two amperes charge per hour, give your battery at least 24 hours to charge fully. Don’t worry if this seems like a long time for the battery to charge fully because this is quite good for the life of the battery.

An automatic charger would turn off when the battery’s charge becomes full. This is good because nothing kills a battery more than overcharging. If you are still working with an old-style charger with no voltage regulator, then be vigilant to turn it off as soon as charging is complete.

10. Place the Battery Back Into the Mower

After you have fully charged your battery and everything seems to be fine, then screw the caps of the electrolyte cells tightly. Once again, have a thorough look at your battery to make sure that everything is fine. There should be no bulging of the sides, no fluids leaking from anywhere, or any cracks and creaks.

Place the Battery Back Into the Mower

When satisfied, lift the battery and place it within the mower exactly as you had taken it out. Carefully reconnect all the wires that you disconnected earlier. While reconnecting, the positive terminal must be attached before the negative terminal. After fully connecting the battery, secure it with screws and straps so it does not jolt around while the mower is working.

11. Start the Engine

Now that the newly cleaned, refilled, and a charged battery is back where it belongs, let’s see if it will work. Connect the spark plug back to the mower that you had disengaged earlier. Push the start button of the engine to get it running.

If the battery has been restored fully, the engine will start immediately without making any sounds. The mower will run smoothly without any hiccups, and there will be no signs of trouble like gasses being produced or jerky engine movements.


Before concluding this detailed guide on battery restoration, here are some key take-home points we must reiterate.

  • Find out where the battery is located within your mower and take it out after disconnecting its terminals.
  • The cells on the top of the mower need to be drained of the fluid in them. Make sure you are wearing the thickest gloves you can find because this fluid can cause severe burns.
  • Before refilling the cells with fresh electrolytes, wash them with a commercial battery cleaning solution or a homemade baking soda solution first.

So far, you have learned how easy it is to restore a battery that has been giving you trouble but has not completely gone bad. Follow all the steps given above while taking care of your safety to make your battery healthy again.

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