Keeping your battery charged is extremely important for its health. Extending battery life is something that is in the best interest of all lawn equipment and power tool owners. This is because there is nobody on the face of the Earth who likes having to replace batteries. It always seems to end up being one big, expensive, pain in the butt. So what’s the deal with overcharging, and can you overcharge a lawn mower battery? The answer to these questions might seem pretty counterintuitive at first, but I’ll do my best to explain what I’ve learned.
Can You Overcharge a Lawn Mower Battery? (The Short Answer)
To make a long story short, yes, you can overcharge a lawn mower battery. Most lawn mowers use lead-acid batteries that will be damaged by use of the wrong voltage power supply or excessive charging. With that being said, rechargeable lithium-ion lawn mower batteries can also be overcharged. To stay on the safe side, it’s best to use a trickle charger/battery tender or automatic charger so that your batteries can’t get overcharged.
How Long is Too Long When Charging a Lawn Mower Battery?
Knowing that you can damage your battery by charging it incorrectly, I’m sure you’re wondering how you can avoid overcharging. To get to the bottom of this, I should probably describe how overcharging occurs first.
Overcharging can happen anytime you’re using a battery charger that doesn’t automatically stop charging once the correct voltage is reached. Charge times vary greatly depending on the type of battery and charger you have, but there is a general rule that you can follow to avoid overcharging.
Basically, don’t hook up a regular battery charger to your battery and forget about it. A lot of people like to leave batteries charging overnight, but it can be risky. These types of chargers are designed to charge batteries as quickly as possible, and they don’t automatically shut off when the battery is charged. If using a normal battery charger, you should check your battery’s voltage every hour or so until it is charged.
There are general guidelines for how long to charge a lawn mower battery, and there are even specific equations you can use to calculate the hours required to charge different batteries at different rates. But, I’m no mathematician so I prefer to take the easy approach and charge my batteries with an automatic or trickle charger.
What Happens to a Lawn Mower Battery When It is Overcharged?
When a battery is subjected to excessive charge for an extended amount of time, bad things happen. The temperature of the battery increases, deterioration of the internal parts occurs, gasses are released, and there is even a risk of fire/explosion. In other words, you will definitely affect how long a lawn battery lasts by allowing it to overcharge. Let’s discuss the consequences of an overcharged battery in a little bit more detail.
Capacity Is Lowered
If you just overcharge your battery a little bit, there might not be any consequences that are very noticeable. For example, a 12-volt battery can actually be charged enough to hold a little over 14 volts without any issue. But, one of the first symptoms of a battery that has been overcharged is a weakened ability to hold a charge. This is true for lead-acid and lithium-ion batteries alike. When a battery is charged too much, corrosion will start to occur which limits the effectiveness of the battery itself.
Temperature Rises & Water Level Lowers
Both lead-acid and lithium-ion batteries will experience an increase in temperature when overcharged. If temperatures get high enough, something called thermal runaway can occur which can cause pretty serious damage.
Thermal runaway is a chemical reaction that basically describes the process of batteries heating up very quickly and uncontrollably. This happens because the more a battery breaks down, the more rapidly it will heat up. In other words, thermal runaway is a sort of exponential increase in the temperature of the battery itself.
As temperatures rise in lead-acid batteries, the internal water that is mixed with the sulfuric battery acid will start to evaporate and can eventually boil. This causes a bunch of pressurization in lead-acid batteries that are often sold pre-assembled and don’t have ventilation.
Toxic Gasses Released
Another consequence of overcharging can be the release of gasses. One of the gasses that is produced by lead-acid batteries is hydrogen gas. If the battery doesn’t have any ventilation, this can pose an explosion risk.
The other type of gas that lead-acid batteries can release is hydrogen sulfide gas. This is another nasty gas that in small amounts can make you sick, and in large amounts can even be fatal.
Potential Bulging, Leaking, Melting, or Fire
Heightened temperatures, the release of gasses, and the breakdown of internal battery components can have an extremely harsh effect on your battery and even your own health in some cases. One of the signs of a battery that has been overcharged is bulging. This is usually caused by a bunch of built-up pressure.
Another symptom of overcharging and pressure buildup is fluid leaking from the top of the battery. This one only applies to lead-acid batteries but it’s worth noting. You don’t want to handle the electrolyte and acid fluid that is stored inside lead-acid batteries by hand.
In the case of thermal runaway and crazy temperature increases, you might even have a melted battery or a fire on your hands. Both lithium-ion and lead-acid batteries can get hot enough to melt and combust. Although, most lithium-ion batteries have a temperature sensor that prevents this.
3 Things You Can Do to Prevent Overcharging Your Battery
Now that we’ve established that batteries can be overcharged and damaged by doing so, let’s get into some of the ways to prevent it from happening. Luckily it doesn’t have to take too much effort to make sure your batteries charge correctly. I think that the best ways to avoid overcharging your battery are: monitoring your battery while charging, using a trickle charger or battery tender, and making an overcharge protection circuit.
Use Automatic Chargers
Having and using the correct charger for your battery makes a huge difference. I’ve been mentioning how helpful trickle chargers and battery maintainers can be here and there, but let me explain why.
Like I said before, trickle chargers slowly recharge batteries and they automatically stop charging once the battery is at the correct voltage. The reason they’re so useful is that they will never overcharge, and they also make maintaining a battery super easy. You don’t want to leave a battery sitting without charge for extended periods of time because the capacity of the battery can also be weakened that way.
Most trickle chargers have a 6 and 12-volt setting, and with these types of chargers you can leave the battery hooked up overnight without worrying about it. You can use trickle chargers for batteries on cars, motorcycles, boats, and a ton of other equipment that uses lead-acid batteries, so it’s a worthy investment.
Monitor Battery and Voltage While Charging
If you really want to stick with a normal battery charger, the best way to make sure you’re not overcharging is to monitor your battery regularly as it charges. I’ve heard of people setting timers that go off every hour, but the key is just to measure the voltage as you go.
Normal battery chargers are designed to charge as quickly as possible so they supply a ton of power at a time. If you’re not careful it can be pretty easy to overdo it.
Be aware that normal battery chargers will charge at different rates, too. Battery chargers usually range from about 2-10 amps, so be sure to factor that into your estimation of how long your battery will take to charge.
Make an Overcharge Protection Circuit
For those of you that are electrically inclined, you could go as far as building a circuit that cuts off the charger from delivering more power once the correct voltage is reached. I can’t claim to know how to build one, but I have heard that they’re super useful.
If you’re in the mood for an interesting DIY project, there are a lot of people that have made their own overcharge protection circuits. If you’re not as excited about this, a battery maintainer or trickle charger will serve a pretty similar purpose.