Can You Overcharge a Lawn Mower Battery?

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Can you overcharge a lawn mower battery? The simple and straightforward answer is yes. You can actually overcharge your lawn mower battery if you charge it beyond the recommended charging duration.

This expert’s opinion from Sears Parts Direct gives an insight into the reasonable charging duration for a lawn mower battery: “The charger should fully charge the battery in one hour at the 10-amp setting. You might have to charge the battery longer if your amp setting is lower.”

Charging your lawn mower battery beyond the stipulated duration for each setting puts the battery at the risk of overcharging.

Consequences of Overcharging a Lawn Mower Battery


Why is overcharging your lawn mower battery not advisable? Below are some of its consequences:

Electrolyte water depletion

The electrolyte water in your lawn mower battery supports charging. Overcharging the battery will deplete the water as it converts the electrolyte water to oxygen and hydrogen. Excessive gassing may result from overcharging.

The excessive charging, in turn, will heat up the electrolyte, resulting in oxygen and hydrogen gas generation. In cases of sealed batteries, the overheating may cause an explosion.

Reduced performance

Overcharging your lawn mower repeatedly will reduce its performance over time. Each case of overcharging harms the battery. Charging the battery beyond the recommended duration time and time will gradually but consistently hurt its durability and overall functionality.

Corrosion is inevitable

A significant part of a lawn mower battery is metals. These metallic parts are prone to corrosion during overcharging. As mentioned earlier, overcharging the battery may trigger the production of hydrogen and oxygen gas.

When these gases react on any of the battery’s metallic parts, the affected part will corrode gradually.  As time passes by, the corroded parts will wear out, rendering the battery unusable.

Increased battery temperature

The increased battery temperature side effect is a no-brainer. Overcharging a lawn mower battery will increase its temperature. If the temperature hits an extremely high value, the excessive heat generated will damage some of the battery’s components. In some cases, an explosion is inevitable.

Shorter life expectancy

Each lawn mower battery has an estimated life expectancy from the initial date of use. Under normal circumstances, the manufacturer expects the battery to serve you for that long. However, that won’t be the case if you overcharge the battery. The battery may pack up way before its expected life span.

Increased water consumption

Overcharging your lawn mower battery increases the concentration level of the battery’s sulfuric acid. To address this issue, you must cool the battery with distilled water. Thus, as the battery’s temperature rises, it requires regular cooling. You need more water to reduce the battery’s temperature as often as necessary.

In the face of the damaging effect of overcharging on the battery, understanding the best charging approach for your lawn mower battery will help your mower battery last longer.

How to Charge a Lawn Mower Battery Properly

How to Charge a Lawn Mower Battery Properly

  • Be Safety Conscious: Don’t jump head-on into charging the battery after getting the appropriate charger or if you have one. 
    Put your safety first before anything else. Wear protective clothing such as safety glasses and gloves to safeguard yourself from any potential danger.
  • Find the battery: You can find the mower’s battery under its seat. The location gives you easy access to the battery. However, if you have difficulty accessing the battery, consult the mower’s operator’s manual for help.
  • Watch the connection: A lawn mower battery has two terminals: red positive and black negative terminals. Watch for the terminals and corresponding cable colors when connecting the cable to the terminals. 
  • Connect the positive terminal first, followed by the negative terminal. If you connect the terminals wrongly, your battery could be toast.
  • Use matching voltages: Ensure that the charger’s voltage matches the battery’s voltage to avoid any incompatibility issues. As a reminder, if you are using a mower produced before 1980, choose the 6-volt option. Otherwise, for post-1980 mowers, select the 12-volt option.
  • If you get the settings and other necessary connection instructions right, plug in the charger to the electrical outlet and start charging your lawn mower battery.

Tips to Help You Avoid Overcharging Lawn Mower Battery


Use the Correct Charger


Lawn mowers use batteries with different ratings. While modern lawn mowers use 12-volt batteries, their counterparts built before 1980 use 6-volt batteries. Undoubtedly, you can’t charge both models with the same charger. The incompatibility issue may damage the charger or the battery.

Your lawn mower may come fully equipped with a charger. However, if you have lost the mower battery or it no longer works well, find the most appropriate replacement charger for the battery. 

Consider the charger’s output

The charger’s output counts too. The mower charger must match the battery’s voltage for proper charging. Go for chargers with output less than 10 amps. They will do a better job than others with higher outputs. Be cautious when choosing the best charger output. Machine Lounge advises: “Be careful, however, because using the fast charging options (anything above 10-amps) can damage the battery.”

Consider the battery’s condition

While experts agree that the best charging duration for a 10-amps setting is about an hour, that’s not carved in stone. The battery’s condition at the time of charging determines the most appropriate charging span.

Machine Lounge advises further: “For example, a totally flat battery may not always get charged adequately at the normal rate and you may have to up it and charge for more hours… Going too low is not an option either for most lawnmower batteries as it could take an eternity to get the battery up and running.”

If the dead battery doesn’t come up after charging for a couple of hours, you may need to replace the battery. Obviously, its weak cells have lost their charging ability.

Use a battery tender

Charging your lawn mower battery with a battery tender is unarguably one of the most effective preventive measures against overcharging. A battery tender charges a battery to full capacity without leaving room for excessive charging.

 When the battery is fully charged, the battery tender will shut off automatically. Overcharging-preventing tenders are otherwise known as trickle chargers.

While you may not intentionally overcharge your lawn mower battery, there are chances that you may accidentally do this. Hence, consider the preventive measures discussed in this article to prevent such an unfortunate incident.

No matter the battery’s power condition, don’t charge it overnight. The consequences of overcharging the battery far outweigh whatever reason that tempts you to do that.

It’s noteworthy that most modern batteries automatically shut off as soon as the battery is fully charged. If your battery comes with this feature, don’t lose sleep over overcharging. Otherwise, avoid excessive charging at all costs.