Lawn owners often complain about their lawn mowers not starting and the short life of batteries. It usually happens when they do not charge the battery correctly. Overcharging damages the battery, while undercharging doesn’t give it enough charge to start the mower.
Charging a lawnmower battery requires extra care. You should be aware of the battery type, the safe charging current, and the correct procedure to follow. Not only does it enhance the battery life, but it also ensures safety from accidents.
Let’s learn how to charge a lawn mower battery the correct way. We will go through the step-by-step process of each battery type to help lawn owners recharge lawnmower batteries safely and without any hassle.
Types of Lawn Mower Batteries
You’ll commonly find three types of batteries in a lawn mower. Knowing the type is important to follow the right charging procedure and take care of the battery.
Lead-acid Battery
Lead-acid batteries are usually found in traditional riding lawn mowers. Just like your car, these mowers use batteries to start the engine.
The batteries do not power the mower. They provide the high amperage required to crank the engines. If they aren’t properly charged, you won’t be able to start your mower. And your mower will sit idle when you actually need it.
If you have an old battery, it will probably have removable caps. You have to periodically top off the fluid with distilled water. On the other hand, most mowers have sealed batteries that do not have caps. They are maintenance-free, which means you don’t need to add anything.
These are the simplest batteries that can be charged with 12V automotive battery chargers. You don’t need to charge them every now and then. Just charge when the battery is extremely low or dead so that it’s unable to start the mower. If you haven’t used the mower for a long time, the battery might have lost some of its charge.
For charging such batteries, you need to ensure the charging current is low. 2 to 4 amps are more than enough to charge the battery without overheating. You have to select a low amperage, depending on the battery size. If the battery is 15-30 Ah, charge it at 2 amperes.
Most importantly, you have to be extra careful while storing them. You must recharge them before storing them in winter. Otherwise, the water inside could freeze, and the plates will be damaged.
AGM or Gel Batteries
Absorbed Glass Mat (AGM) or Gel batteries are commonly found in zero-turn mowers. They are completely sealed, so there is no chance of spillage. They can tolerate the vibrations of the mowers and ups and downs on uneven terrain. They do not require any maintenance and are much better than lead-acid batteries.
The reason for no spillage or leaking is that there is no free-flowing liquid. It is absorbed into fiberglass mats (AGM) or suspended in a gel (Gel batteries). And that’s also the reason behind their name. They follow the same chemistry as a lead-acid battery; the only difference is the way the acid is housed.
Another benefit of these batteries is low self-discharge. Which means they can hold the charge for a longer period and hardly lose about 1-3% of their capacity per month when sitting idle.
Charging both AGM and Gel batteries requires extra care. They are highly sensitive, and you can ruin them with one mistake. The reason is that these batteries are completely sealed and have pressure-relief valves for safety purposes. Once these valves are opened in any emergency, the internal capacity drops immediately.
If you charge it at a high voltage level, the battery will produce too much gas, which will lead to internal pressure build-up. The pressure-relief valve will open to let the gas escape. The battery dries out completely as it produces more gas than it can recombine into water. And once that happens, the battery is ruined because it is sealed, and you cannot add more water to it.
Simply put, you cannot charge these batteries with your old automotive chargers. They can destroy the battery by overcharging and high voltages. The best solution is to use a Smart Charger that limits the maximum voltage and adjusts the current according to the battery status. It prevents the gas build-up and keeps the battery safe.
Go with a smart charger specifically designed for AGM or Gel batteries and charge them at a lower current. A current of 2 amperes or lower is preferred for long battery life.
Lithium-ion Batteries
Lithium-ion batteries are much more advanced compared to lead-acid batteries. They can either be used to start the engine or power the whole mower completely.
You might have seen battery-powered mowers. They use lithium-ion batteries to power the whole operation. While in some riding mowers, lithium-ion batteries are used to start the engine.
They are superior in performance. Firstly, they offer consistent power until the battery is fully discharged. This is not possible in lead-acid batteries, as they lose power as the battery drains.
Secondly, lithium batteries have negligible self-discharge. Even if you put them in storage for six months, they will hardly lose 5% of the total charge. Thus, they hold charge for a longer period. Lastly, you can quickly charge lithium batteries. The reason is that they can bear a high current that fully charges the battery in a minimal time.
However, you can’t charge a lithium battery like a normal one. If you push a steady voltage directly through the terminals, it will overcharge the cells. It will increase the internal temperature rapidly and cause a short circuit, which is called Thermal Runaway. It causes an aggressive chemical fire that cannot be extinguished easily with water.
That’s why lithium-ion batteries need a Battery Management System (BMS). It’s a circuit board that controls the charging of each cell. If one cell is completely charged, it redirects power to other cells.
It protects the battery from overcharging and instantly shuts off when the cell reaches its maximum voltage capacity. It also monitors the battery pack’s temperature and only charges it when the temperature is in the safe range.
How to Charge a Flooded Lead-Acid Battery
Step 1: Inspection
Before charging a lead-acid battery, inspect it for any damage. Also, check the fluid levels in old batteries with caps. If any cell’s fluid is low, you can add distilled water.
Always charge a lead-acid battery in a well-ventilated space. It releases a small amount of hydrogen gas, which is flammable, and it can be catastrophic in small spaces.
Step 2: Terminal Cleaning
Clean the terminals of the battery. You can clean it with a cloth to remove dust and debris. It’s necessary for a tight connection.
But if there is a white-and-green layer, oil, or anything else, you should prepare a solution for cleaning. Mix one tablespoon of baking soda in a cup of warm water. Dip a toothbrush or a wire brush into the mixture and clean the terminals. Wipe off the residue with a clean cloth.
Step 3: Connect Clamps
If the battery is still on the mower, make sure the mower is turned off. A better option is to take out the battery for recharging.
Do not plug in the battery charger at this moment. You need to connect the clamps first. Connect the Red (Positive) clamp to the positive terminals of the battery. Then, connect the Black (Negative) clamp to the negative terminal of the battery. Always follow the sequence.
Step 4: Select Settings
Now, you need to select the settings on the charger. The voltage should be 12V, while the current should not be more than 2-4 amps.
Step 5: Double Check
Before you plug in the charger, double-check that the charger clamps are connected to the right terminals.
Often, people do it wrong and end up causing a heavy spark, blowing the fuse, and damaging the charger. In the worst case, it can ruin the battery or cause an explosion/fire.
Step 6: Plug-in and Monitor
Plug the charger into a wall outlet and turn it on. If you have a smart charger, it will automatically charge the battery. When the battery is fully charged, it shifts to Trickle mode to maintain the battery voltage without overcharging it.
If you have a manual charger, you need to monitor it and turn it off before it starts overcharging. Attach a DC voltage meter to the terminals. You can also use a multimeter.
Monitor the battery voltage. When it’s fully charged and disconnected from the charger, it should show 12.6V. Keep in mind that the charging voltage is usually higher than that, so turn off the charger to know the right voltage.
Step 7: Disconnect
When the battery is full, turn off the charger. Unplug it from the wall outlet. Disconnect the Black (Negative) clamp first and then the Red (Positive) clamp.
How to Charge an AGM or Gel Battery
Step 1: Use a Smart Charger
A smart charger is mandatory to charge AGM or Gel batteries. It will recharge the battery at the optimal voltage without building up any gas inside or causing harm to the battery.
You don’t need to monitor recharging as the charger monitors internal resistance, temperature, current state of charge, etc. It knows when to stop recharging.
Step 2: Connect the Clamps
Once you have a smart charger, you can connect the clamps to the battery. Make sure the terminals are clean. Use a cloth to clean the dirt and debris.
Attach the Red (Positive) clamp to the positive terminal of the battery. Then, attach the Black (Negative) terminal to the negative terminal of the battery.
Step 3: Select the Settings
On your smart charger, select the AGM or Gel setting. Set the maximum amperage to 2 amps or lower. Never go with a higher current than necessary, as it will degrade the battery.
After setting, let the charger do its job. It will initially charge the battery in the bulk mode and apply the maximum current selected. Once the battery reaches about 80% of the charge, the charger reduces the current and charges the battery slowly.
When the battery is fully charged, the current is dropped down to a safe standby level. It maintains the required voltage without generating heat or overcharging. Even if you reach hours late after a complete charge, the battery will still be at the optimal voltage.
Step 4: Disconnect
Finally, turn off the charger and remove it from the outlet. Remove the Black (Negative) clamp first and then the Red (Positive) clamp.
How to Charge a Lithium-Ion Battery
Step 1: Remove the Battery and Inspect It
Make sure the mower is turned off. Press the battery release latch and take out the lithium-ion battery from the lawn mower.
Inspect for any damage, such as cracks or swelling. If the battery is perfect, you are good to go.
Step 2: Use the Right Charger
For lithium-ion batteries, you must use the manufacturer’s recommended charger. You might have received it along with the mower or as an extra purchase.
Never use an automotive battery charger or power supply to charge lithium-ion batteries. It will overcharge the battery and cause it to explode and start a fire.
The manufacturer’s recommended charger is perfectly designed according to the battery’s BMS. It knows how to maintain the optimal charging voltage, avoid overcharging, and ensure safety.
Place the charger on a hard and non-flammable surface. It should be a well-ventilated space. And keep away from the flammable and combustible items.
Step 3: Check Temperature and Insert the Battery
Lithium-ion batteries should not be charged if their temperature is high. If you have recently mowed under hot weather conditions, let the battery sit in a shaded and well-ventilated area for half an hour. It will reduce the battery’s temperature.
Slide the battery onto the charger. There should be a dedicated slot to insert the battery. Make sure it perfectly clicks into its place.
Step 4: Plug in the Charger
Plug in the charger and turn it on. It will start charging the battery. Chargers usually have LEDs to indicate the charging status. You will see a red or flashing light if the battery is being charged and a solid-green light when it’s fully charged. You can refer to the user manual of the mower/charger.
Once the battery is charged, you can remove it. Even if you leave it on the charger, the BMS will prevent overcharging and keep the battery safe. However, it’s better to remove it to avoid high voltage stress on cells.
Step 5: Remove the Battery
Unplug the charger from the socket. Then, remove the battery safely. Your battery is fully charged and ready to be used on the mower.
Switch to a Robot Lawn Mower and Say Goodbye to Manual Charging
We have discussed how you can charge different lawn mower batteries, but you have to bear the hassle of removing batteries, connecting them to the charger, plugging the charger into a wall outlet, monitoring the process, and then disconnecting the battery. All this takes time and effort.
A robot lawn mower does not require human assistance for recharging. It mows the lawn, and when the battery charge is low, it returns to the charging station. It recharges automatically and then is ready to mow again or resume the previous task.
It’s an absolute time saver. You don’t have to worry about overcharging, constant monitoring, or following the best practices to charge the battery because it’s completely automated. Even if you are not at home and the mower is working, it will return to the charging stations on its own.
Modern mowers use extremely precise navigation technologies, including NRTK, LiDAR, and Vision, which help them navigate to the charging station no matter where they are.
Not only that, but robot mowers are completely autonomous. They mow your whole yard on their own. You just have to set the schedule and desired mowing height. They precisely cover the area around obstacles and ensure the safety of children and pets.
Thus, you can save a lot of time with a robot lawn mower. It keeps you from doing the intensive chore. You can spend that time in the gym or with family. It keeps the lawn perfectly manicured year-round.
For small lawns up to 0.25 acres, you can select the Navimow i2 AWD series. It’s an affordable mower with incredible features. If the lawn is medium-sized with a complex setting, the Navimow H2 series is an ideal option. For lawns up to 1.5 acres, you can go with the Navimow X4 series, which works on difficult terrain, steep slopes, and mows every corner and edge.
Final Words
Before you start recharging a battery, make sure you know what type of battery it is. It could be a lead-acid battery, AGM/Gel battery, or Lithium-ion battery. We have explained what these different batteries are, their charging process, and how to take care of them. Along with that, we have also explained the step-by-step process to recharge these batteries without any hassle. And if you want to get rid of recharging mower batteries, switch to a robot lawn mower and automate lawn mowing.
FAQs
Can you recharge a dead lawn mower battery?
Yes, you can charge a dead lawn mower battery. Inspect for visual damage first. If it is fine, you can try charging it. Recharge for an hour and check the battery voltage. If it has increased, it means the battery could be saved. Charge the battery completely and then test it on the mower. If the battery can hold the charge, it’s alive, but if it can’t, it’s time to replace it. Often, the battery’s voltage cannot reach 12.7V; it stays under 11V even after hours of recharging. It indicates internal cell damage.
Can you charge a lawn mower battery with a car charger?
Yes, you can charge a lead-acid battery with a car charger. Connect the battery properly and set the charger to a low amperage, such as 2 amps. An automatic charger will fully charge the battery and shut off. If you have a manual car charger, you must monitor the battery voltage and unplug when the voltage is 12.6V or 12.7V. Never recharge an AGM/Gel or Lithium-ion battery with a car charger, as it could ruin the battery and is extremely dangerous.
What is the life of a lawn mower battery?
A standard lead-acid battery could last 3-4 years. An AGM/Gel battery lasts up to 4-5 years. Lithium-ion batteries can last up to 5 years or more, depending on the total number of charging cycles.
Can I charge a lawn mower battery overnight?
If you are using a smart automatic charger, you can charge the lawn mower battery overnight. They automatically charge the battery and switch to trickle mode once the battery is fully charged. Never leave a lawn mower battery overnight while using a manual charger. It will overcharge or ruin the battery. However, in any case, it’s not recommended to charge a lawn mower battery overnight. It’s better to charge during the day and monitor it.
