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Can You Overcharge A Lawn Mower Battery? Or Is There A Cut-Off?

Written by William
Last Updated on March 8, 2021

Is It Possible To Overcharge a Lawnmower Battery?

Lawnmowers nowadays tend to use a 12V lead-acid battery to power there mowers, this battery can be charged easily with a typical charger but might take a while to reach full charge.

This long charging time can leave the temptation to keeping your battery on charge overnight but puts you at the risk of 'overcharging' your battery.

So you might be wondering, can you overcharge a lawnmower battery? And what will happen if you do?

Well, the answer to this question is, it is very possible to overcharge a lawnmower battery, but only on older models which tend to use a 6V battery instead of a 12V. Most modern mowers come with an automatic cut off point that stops taking anymore charge when its battery is at maximum charge.

So as you can avoid overcharging your mower's battery, we will list out how to charge a lawnmower battery below and the consequences that come with overcharging, as well as tips to prevent it from happening in the future.

What Will Happen If I Overcharge My Mowers Battery?

If you happen to overcharge your mower's battery then the electrolyte water inside of the battery will end up turning into hydrogen and oxygen gas.

This gas will leave through the venting system in your battery and can cause sulfuric acid to concentrate and potentially damage the battery of your mower.

The overheating and overcharging can lead your battery to stop charging efficiently and even explode in worst-case scenarios.

Other Effects Of Overcharging Your Mowers Battery

Apart from the worst effects of overcharging such as an explosion, other less severe consequences can happen from overcharging your lead acid battery for your mower.

We have listed a few out below so as you can recognise if you have overcharged your mower's battery or not.

High Temperature

Due to overcharging the mower's battery, there will be an inevitable heat build-up inside of the battery that can cause severe damage to the components inside.

Most modern batteries however have a mix of gases that stop this overheating from happening as a safety measure.

Corrosion Damage

The positive battery plates are likely to get corrosion quickly due to them being made out of metal. This happens because the temperature inside of the battery gets hotter and lets the hydrogen and oxygen escape, creating corrosion and making it harder to cool your battery down.

Reduced Lifespan

Overcharging your battery will hurt its performance and reduce its overall lifespan. This can stop the battery from charging properly again and even make it dead.

Higher Water Consumption

As the sulfuric acid will be concentrated inside of the battery due to overcharging you will need to use distilled water to cool it down. This means the battery will need more and more water as the temperature rises.


A mix of sulfuric acid and distilled water can rise in temperature and potentially melt the housing of your battery, along with the oxygen and hydrogen which will escape, meaning if there is an electric spark, the battery could explode.

How To Charge a Riding Lawnmowers Battery

Now we have got all the scary stuff out the way, we will list some short and simple steps that will tell you the correct way to charge a riding lawnmowers battery below, as this differs from the normal chargers that come with a push or self-propelled mowers.

  • Step One - Put on protective clothing and disconnect your batteries charger.
  • Step Two - Find your mower's battery, many are located under the seat of your mower.
  • Step Three - Connect the positive side of your mower's battery first to the red cable.
  • Step Four - Then, connect the black side of your cable to the negative side of your mower's battery.
  • Step Five - Match the voltage of your charger setting to your batteries which should be 12V.
  • Step Six - Plug the battery charger in and keep an eye on it till it fully charges then disconnect to prevent overcharging, however, most models will have an auto shut off.

Tips To Stop Overcharging From Happening

If your battery is one of the old types and is at risk of being overcharged, then you might need to follow a few tips and tricks to prevent damaging your battery.

We have listed some worthwhile tips below that could be worth noting if you want to try and stop your battery from getting overcharged.

  • Don't charge the battery to full regularly - Charging your battery to the maximum regularly could shorten its life span, instead, it's better to charge it fully only now and then.
  • Use a trickle charger - A trickle charger is a great way to keep your battery charged without overcharging as it makes sure to charge it very slowly.
  • Make sure the battery is kept full when you are not going to use it - If you are not going to use your battery, charge it once beforehand fully.

How Long Does It Take To Charge a Lawnmowers Battery?

Another way to prevent your lawnmowers battery from becoming overcharged is to work out how long it takes to charge it.

On average, lawnmower batteries can be charged in a time from 2-24 hours depending on the charger output and capacity of the battery.

To get an average figure, you can take the amp-rating and amp-hours then perform a simple calculation to work out how long it will take to be charged.

For example, if a 200 amp hour battery is charged by a 20 amp charger it will take 20 hours, give or take to charge up fully.

Always remember to not charge your battery too often, and let it run out then charge it fully, rather than keeping it maximum charged at all times.

Frequently Asked Questions About Overcharging a Lawnmowers Battery

Should I charge my lawnmowers brand new batteries before I use them?

It's best to give your battery a charge before using it when it's brand new out of the box, this can stop the 'memory effect' from happening which is when your battery gets used to charge to a single point and will not want to charge up to its full potential.

What is a trickle charger? 

A trickle charger is in simple terms a very slow battery charger, which allows you to keep charging your lawnmowers battery at a very slow rate, this can be great to use when you are leaving your battery on charge over winter and don't want your battery to go flat.

How can I cool down an overcharged battery?

You can attempt to cool down an overcharged battery by using distilled water, but even then, you have to take caution not to pour too quickly and end up overheating the battery even more.

Final Words

To conclude, overheating your lawnmowers battery is a rare thing to do if you have a new 12V lawnmower, as they have a safety stopper in place which will stop the battery from taking more charge as it gets full.

It's always best to work out how long it will take to charge your battery before leaving it on all night, and you should use a trickle charger when possible to keep your battery in the best health when not in use.

About the author
Written by William
I have always had a passion for gardening and that with a background in selling lawn mowers for the past 10 years, I have become very knowledgeable in all types of gardening tools. The site was created as a hub where I can review and write about all of the tips around gardening.
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