How To Restore A Lawn Mower Battery (An In-Depth Guide)


Suppose you didn’t use your lawn mowers for an extended period, and you encountered some battery issues at the time of mowing. So, it can be due to the accumulation of lead sulfate crystals or the faults of the cell.

Now, are you thinking of buying a new one?

But why will you purchase a new one if you know how to restore a lawn mower battery! The majority of lawn mower batteries are lead-acid batteries. You can recondition the batteries by using Epsom salt and distilled water.

Around 99 million wet-cell lead-acid batteries are manufactured per year. These batteries contain heavy metals like lead, mercury, nickel, and cadmium. So, if these are not disposed of properly, they can be detrimental to the environment. Therefore, it will be witty to recondition the battery to save both your pockets and your environment. 

Why Won’t My Lawn Mower Battery Hold A Charge?

Within the 12v lawn mower battery, the lead plates are immersed in sulfuric acid. As a result, various phenomena can upset the chemical balance of the battery, like contamination, loss of acidic electrolyte, or lack of proper recharging.

Generally, when the chemical reactions occur, both lead plates of the battery convert into lead sulfate. When you use the battery regularly, the discharge and recharge make opposite chemical reactions and balance the anode and cathode plates. But when this lawn mower battery is left discharged for a longer period, lead sulfate crystals form. These crystals reduce the surface area of reactions and thus minimize the capacity.

There are some other causes as well. For example, a lawn mower battery may last around four years. So, when it is towards the end of its lifespan, it will not hold its charge like the previous.

If the engine of your lawn mower is running too slow or has a too low RPM, the battery also can’t deliver its best and will not be able to charge fully.

Sometimes the alternator fails to work for the damage of the rotor inside it.

How to Know When a Lawn Mower Battery is Dead?

There are several ways to know if the battery is working or not –

  • If you turn the key on of your mower and the engine cranks slowly or is making a clicking noise, your lawn mower battery may be dead.
  • The water level may not be full, and that’s why the battery is dead.
  • You can use a multimeter to test the battery’s voltage.

Set the multimeter to DC. You need to put the red probe to the positive end and the black probe to the negative end simultaneously. See whether it reads lower than 11.8v (30%) in an open circuit.

If it goes lower than 11.8v, you will need to restore it. 

Tip: Always give your battery a full charge to ensure longevity of your battery.

How Do You Recondition A Lawn Mower Battery?

When there is a build-up of lead sulfate crystals, the battery will encounter a chemical imbalance in the electrolyte.

Fortunately, you don’t have to spend a lot to recondition the battery. Instead, you can do it with some inexpensive ingredients available at home.

You will need a solution of magnesium sulfate. However, you need to remember that it will not repair a battery fully, but it will definitely repair it to around 75 to 80% of its original state and help you use it for more years without having to dispose of it.

The things you will need –

  • Your damaged lawn mower battery
  • Battery charger
  • Epsom salt or magnesium sulfate
  • Distilled water
  • A dropper or syringe 

Tip: Since the acid is corrosive and the electrolytes are poisonous, you need to wear personal protective equipment to avoid any sudden accidents.

The Steps You Need To Follow

Removing the Caps

When you take the battery out of your lawn mower, you will see battery cells on the top of the battery. There will be caps on top of the cells. Use a flat screw to remove the caps.

Checking the Acid Level

After the first step, you will need to get to the battery acid. Now take a syringe or dropper and cautiously remove the acid until the cells are 50 to 60% full. Again, make sure that you are not messing up this liquid, and remember not to drain too much.

Making a Solution of Magnesium Sulfate and Distilled Water

When you are done with the previous step, it is now time to make a saturated solution on the stove by using distilled water and Epsom salt or magnesium sulfate.

When you have prepared the solution, it is now time to fill each of the cells with this solution by using a dropper.

Charging the Batteries

You have to charge it if the above process is done. You have two ways to charge your battery – either use a battery charger or using the alternator. For the alternator, you need to reinstall the battery to the mower, jump start it, and ride the mower for one to two hours to let the battery get charged.

Now you can use your restored battery for more than 4 to 6 months. You may have to repeat the process until the battery is no longer effective.

Tip: Always remove the battery from the mower while storing it for a long period. 

Should You Replace The Battery?

Replacing a battery has both upsides and downsides. Check out them before determining the replacement of your battery –

Advantages: Shortcoming:
gives more power to the engine for the strong ignition Increases the environmental pollution
Reduces the worry of a sudden death of the old battery. Needs an investment
Minimizes the maintenance

Follow This Guideline:

 Ending Notes

Since we now know how to restore a lawnmower battery, we should imply it in our daily life. The disposal of the batteries increases the greenhouse gas effects, the consumption of natural resources, photochemical smog pollution, ecotoxicity, air acidification, and so on.

Let me know in the comment section about your experience in restoring the battery of your lawnmower. Also, let me know whether you like to replace your battery or recondition your battery.

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