If you are curious about the symptoms of a bad lawn mower battery, the nyou are among the thousands of gardeners who have this question in their minds. The good news is that most symptoms are hard to miss, such as clicking noises and rotten eggs smell.

Bad Lawn Mower Battery

In this complete guide, we will discuss all the symptoms that indicate that your battery might be struggling. Carry on reading because we will also discuss changing the electrolyte fluid in the battery to make it last longer.

What Are the Symptoms of Your Lawn Mower Battery Going Bad?

The symptoms of your lawn mower battery going bad include the engine not starting, the mower producing clicking noises and a rotten egg smell, the battery losing charge faster than normal, the mower refusing to cut grass, and poor fluid levels.

It is easy to tell if your lawn mower’s battery has gone bad. Some classic tell-tale signs of such a battery are that the engine won’t start, produce clicking noises and produce toxic fumes.

– The Engine Won’t Start

The first tangible sign of a bad battery is when the mower won’t start on the first pull. Even more, multiple ignition turns might be needed to get the engine fired as the situation worsens. This means the engine does not have adequate strength to fire the spark plug.

After multiple tries, it does so feebly when the engine fires up. It will crank much more slowly than normal, sometimes not at all. However, the engine not starting can also be due to a faulty spark plug, ignition button, or alternator. Make sure to check these out to see that they are working properly before moving on to the battery.

– Produces Clicking Sounds

A lawn mower is not supposed to make unnecessary sounds while working, so if it starts producing clicking sounds when you attempt to turn it on, the battery is running low on power. Recharging it properly might solve the problem.

Reasons Bad Lawn Mower Battery

Sometimes, the mower produces clicking noises and starts but does not turn over. This might mean that the battery is completely dead and in need of a replacement. When the lawnmower battery gets bad because of freezing and extreme weather conditions, this could cause problems with clicking and the engine starting without turning over.

– Produces a Rotten Smell After Some Use

A bad battery gets heated soon after use and produces toxic fumes. This is more pertinent for lead-acid batteries, where the sulfuric acid in the electrolyte gets turned into toxic fumes once the battery heats up.

In most of these cases, you will be able to smell hydrogen sulfide immediately because of its rotten egg smell. Be careful when touching the mower where the battery is located as it will be quite hot. Turn the engine off and let the mower cool down before doing anything else.

– The Battery Loses Charge Quickly

A lawn mower battery that either does not charge fully or stays charged afterward is going bad. Either the battery is too old or damaged, or there is something wrong with the charger.

With time, the battery’s capacity to hold charge does decrease naturally. After some years, you might notice having to charge it more often than before. However, if the battery is new or seems to be losing charge abnormally fast, then this is problematic.

If the battery refuses to charge altogether, in this case, your charger is faulty or the battery has gone bad.

– The Mower Refuses To Cut Grass

One uncommon and often ignored symptom of a gas-powered lawn mower’s battery going bad is that it will no longer be as efficient as before. It might work fine on thin, wispy grass, but as soon as you try to cut tall, thick grass, it will give up.

The battery is not strong enough to provide the engine with the power to cut through resistance. Check your blades to ensure there is nothing wrong with them, like a need for further sharpening. If they are okay, the battery is going bad and you need to fix it.

– The Battery Appears to Bulge

In riding mowers, the battery is usually located under the seating area and charged without taking it out of its box. That is why people often need to pay more attention to this vital symptom that the battery could be better.

When the engine stops turning off or producing clicking noises, take the mower’s seat off and take the battery out. It would help if you unscrewed some nuts and bolts here and there to loosen it. Notice the classic signs of battery wear down on all sides, including the bottom.

These signs include cracked edges, bulging sides, and blue-green corrosion on each battery terminal. Have a mechanic look carefully at this battery in case it becomes a health hazard.

– Poor Fluid Levels

Fluid levels within the battery are important indicators of a healthy vs. bad lawn mower battery. Check the fluid levels within each cell of the battery for this. In the case of lead-acid batteries, the electrolytes are a mixture of water and sulfuric acid.

Many things disturb the delicate balance of fluids within the electrolyte, such as overuse, overcharging, physical damage, or a battery that is too old. If the fluid levels within the battery are low, it is in an apt condition.

If the rest of the battery is in good condition, restoring the fluid levels will improve the battery. Buy a couple of bottles of distilled water and use them to get your battery working again.

How Do You Improve a Bad Lawn Mower Battery?

To improve a bad lawn mower battery, you should first assess the condition of the battery and conduct a voltage test. Prepare the tools that you will need and carefully remove the battery. Next, clean the battery and fill it with fresh electrolyte.

Solutions Bad Lawn Mower Battery

Unless the battery is completely dead, you can help improve its condition by cleaning it and changing its electrolyte fluid. Instead of buying expensive fluid from the market each time, make your electrolyte at home using Epsom salt and distilled water.

1. Assess the Condition of Your Battery

Before deciding whether to change or repair the battery, assess it thoroughly. First, ensure that each cell is filled with the electrolyte until the line.

Then give the battery a detailed examination to see if it is corroded, cracked, leaking, or bulging from anywhere. If any of these symptoms are present, then it is better to discard them for a new one.

2. Conduct a Voltage Test

A voltage test will determine whether or not the lawn mower’s battery is dead. Most lawn tractors and lawnmowers use a 12-Volt battery to run them. A fully-healthy 12-Volt battery, when fully charged, will display a voltage of around 12.6 to 12.8 Volts.

In case of an older mower with a six-volt or lower battery will also display a voltage of six volts when it is completely charged. You will need a multimeter to check this voltage. If there isn’t one present at home, borrow it from someone or order one online as they are pretty cheap.

Attach the multimeter to the battery and set it at DC at 13 volts. The meter’s red lead should be attached to the battery’s positive terminal, while the black lead goes to the negative terminal. The battery has gone bad if the meter reads less than 12.3 volts. If the voltage comes out fine, then proceed to the next step.

3. Prepare the Tools You Need

Use your safety goggles, full-sleeved clothing, and thick rubber gloves when dealing with the lawn mower engine and battery. Make sure your battery charger is functional, automatic, and has an in-built voltage regulator. 

Find baking soda and distilled water at home or in your local supermarket. A plastic funnel is also a must-have item. Epsom salt (magnesium sulfate) is the last ingredient you will need.

4. Remove the Battery First

Turn the engine off, pull out the keys, and disconnect the spark plug. Around 90 percent of riding-style mowers have batteries under the driver’s seat. Pull up the seat, loosen the screws holding the battery in its chamber, and carefully pull it out.

For any other type of mower, consult the instructions manual to see where the battery is located. Disrupt the negative and positive terminals to remove the battery from its chamber first.

There will be caps on each battery cell which need to be removed. Usually, they will be located right on top of the battery and easily come off. Otherwise, a small flathead screwdriver will help you uncap the battery.

5. Clean the Battery

If the battery terminals have bluish-green corrosion, clean them first. A corrosion-cleaning solution with sandpaper will help clean the discoloration. The next step is to drain out all the existing fluid from the battery.

The insides of the battery need to be cleaned from sulfate buildup over the years. Measure 10 ounces of baking soda and dissolve it in one whole gallon of distilled water. Using the funnel, pour this solution into the empty cells of the battery and put their caps back on.

Now shake your battery thoroughly and leave it for a minute or two, then drain the solution out using the same funnel. Make sure you wear the thickest rubber gloves you have because these solutions can burn the skin.

6. Fill the Battery With Fresh Electrolytes

Now that it is clean, your battery needs fresh, new electrolytes added to it. You can buy electrolytes premade or make it yourself at home. It is simple, and you only need to add 15 ounces of Epsom salt to one gallon of distilled water.

Warm the water a little bit first, so the salt dissolves quickly. Again, the funnel will be helpful while pouring the electrolyte into each battery cell. There is a line on each cell until you fill it. Be mindful that you don’t overfill or underfill the battery. Screw the caps back on each cell, and your battery is ready.

7. Recharge the Battery

Next, it’s time to recharge your newly filled battery for the first time. Always use automatic chargers with adjustable settings options for charging.

Set the charger to the slowest charging option, around two amperes per 24 hours. Yes, it would help if you gave the battery at least one whole day to become charged. During this time, keep the caps on individual cells slightly loose for any potential outflow of the charge.

Once the battery is charged to 100 percent, tighten the cell caps. Carefully place the battery back in its place within the mower. Attach the positive terminal and then the negative one when connecting the battery to the mower.

8. Check the Connections

Before restarting your newly charged battery again, check that all its connections with the engine are correct and secure. The negative and positive terminals should be attached properly to their required connections. If broken or damaged, the cables will not let the engine start, so it is better to replace them.

why Lawn Mower Battery Bad


Before we conclude this article, here are the most pertinent points regarding a bad mower battery.

  • The first sign of a bad battery in the mower is that the engine will have a harder time starting and producing sounds while working.
  • Bad batteries lose charge rapidly and need frequent recharging. They also produce toxic gases and fumes, such as hydrogen sulfide, that smell like rotten eggs.
  • A bulging, cracked, or leaking battery is also symptomatic and needs to be replaced immediately.
  • If the battery is not dead, then take it out, clean it, and replace its electrolyte with a fresh one.

When the mower battery gets old, you must be careful about potential symptoms if it doesn’t work as well as before. This would ensure that you improve its condition or change it before it becomes a potential health hazard.

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