How to Install a Lawnmower Battery, step by step


Gas-powered lawn mowers with an electric starter need a battery to provide the power to start the engine. The battery also supplies energy for all other electrical functions, such as headlights and other attachments. Lawnmower batteries are rechargeable and can be used for long periods. But after many years of performance, the battery loses its capacity. It has difficulty holding and store the charge, rendering it obsolete. In this case, it must be removed, and a new battery has to be installed in its place.

How to install a lawnmower battery, step by step:

  1. Check the current model of battery and buy a replacement.
  2. Unplug the old battery
  3. Remove your old battery’s terminals
  4. Install the new battery
  5. Connect the new battery’s terminals

You can always employ a mechanic to replace your lawnmower battery, but installing it yourself saves you time and money. Replacing a lawnmower battery is very easy and not really different than changing the car battery. It is important to remember that not all lawnmower batteries are the same and differ from model to model. So, make sure you select the suitable type and size for your lawnmower. Details on the type of battery can be found in the owner’s manual.

We have divided the whole process into 12 steps. This will make replacing and installing easier and ensures that no battery terminals are damaged during the process. Let’s dive into the details for installing a lawnmower battery.

Step-by-Step Installation of a Lawnmower Battery:

The 12 steps will cover the replacement of your lawnmower battery.

● Step 1: Make the cleaning solution

Before starting with the removal of the old battery, we first make some cleaning solution to clean the battery compartment. Place 1 tsp of baking soda in a cup of water in a disposable cup. To dissolve the baking soda, mix thoroughly with a spoon. We found that this really cleans it well, but you can use something else as well.

● Step 2: Prepare the Lawnmower

Park your lawnmower on a clear, flat surface. Make sure the ignition key of the mower is in the off position. If it is not, turn it off and take the key out. Allow the blades and all other moving parts to stop, and let the mower cool down for some time. Disconnect the blade using the blade engagement lever, set the parking brake on, and ensure the transmission is neutral.

● Step 3: Locate the battery compartment

Find the battery compartment in your lawnmower. The battery compartment is normally under the seat or hood for riding lawnmowers.

For push mowers with an electric starters, the battery is usually placed on the back or the top of the deck in a black box by the handle.

● Step 4: Detach the old battery

The next step is to unplug the old battery from its terminals. The battery’s negative terminal has a “-” symbol on it, and the black battery cable is attached to it. The battery’s positive terminal has a “+” symbol, and the red battery cable is attached to it.

Relieve both the negative and positive terminals of the battery using the adjustable wrench by rotating it clockwise. When the terminals are loosened, pull and detach each battery cable from the old battery.

● Step 5: Detach the old battery

Pick up the old battery from the middle handle to detach it from the battery case. Set aside the old battery. Clean the battery compartment or the rag box, dipped in 50-50 baking soda solution, in water. Use the dry side of the fabric to dry the compartment.

● Step 6: Take care of corroded terminals

There is often corrosion on the battery terminals that connect the battery cables to the terminals. Use some cloth dipped in the mixture of the baking soda that you prepared earlier, and use it to clean the battery terminals and dislodge the corrosion.

If your lawnmower has a bracket to secure the battery, you need to loosen it and shift it to one side. To do this, insert a flat-head screwdriver in the bracket and rotate the screwdriver in the counterclockwise direction to loosen the screw and shift the bracket to one side.

● Step 7: Clean the ends of the terminal

Make sure that the terminal ends of the battery cables are clean. To do this, insert the battery terminal cleaner’s pointed end into each battery cable and form the cleaner into circles to eliminate corrosion and dirt. Corrosion can have a significant effect on the power that lawnmower will get from the battery. Clean both cables until both circles are clean and shiny inside. Use a shop towel to clean off excess metal shavings, if any.

● Step 8: Get the appropriate replacement battery

Ensure that the new battery fits the old one in weight, size, power, voltage, and terminal positioning.

Insert the new lawnmower battery in the battery compartment. To keep the new battery terminals from forming corrosion, apply a thick layer of petroleum jelly to the terminals.

● Step 9: Connect the new battery to the terminals

Attach the red battery cable to the new battery’s positive terminal and tighten it with an adjustable screw. Do the same step for the negative terminal and the black cable.

● Step 10: Make sure that the battery is fixed correctly

If your model has a bracket to keep the battery in place, connect it back on and tighten the screw.

● Step 11: Removal of the old battery

Batteries are harmful, so the old battery needs to be disposed of properly. For this purpose, take your old battery to an automobile service station, a recycling center, or a car parts shop.

● Step 12: You’re all set to start the lawnmower

Now, start the lawnmower by pressing the key. If it starts in the normal way, the new battery has been correctly installed.

Suggestions and remarks Regarding battery installation:

● Suggestions:

  • Check the battery specifications: As described above, the battery type is particular to the build and model of the mower. Use the battery perfectly suited to your mower for the best results. Details on the battery can be found in the owner’s manual. You can also check the details that are on the old battery. Measure the size as well, so you know that the new one will fit.
  • Corrosion: Check the corrosion on your battery terminals at least once a month.
  • Maintenance of the battery: Check the user manual for information on the battery’s correct charging and maintenance. Ensure proper charging and maintenance for optimum output and better battery life. If you winterize your lawnmower, or you plan to store it for an extended time. It is best to remove the battery and use a battery maintainer to keep it in optimal condition.
  • Battery holder: Ensure that the holder of the battery is clean and dry. Remove corrosion and debris from the holder and keep it dry if the holder is made of metal with sand and paint as fumes coming out of the battery can contribute to rusting.

● Remarks:

  • Protection against corrosion: Do not allow any moisture or water to enter the battery cells when rinsing off corrosion.
  • Pull the cables gently: If you forcefully pull off the cables, the connecting terminal can be switched off. So, pull the cables down gently.
  • Short circuit: do not touch the battery cables to any other metallic part of the lawnmower when removing and replacing them. Otherwise, the sparks can fly and cause the battery to discharge.

Diagnosing the lawnmower battery:

One reason why a lawnmower cannot start is that the battery does not have enough power anymore. This problem can be diagnosed easily with the help of a digital multimeter.

● Step 1: Locate the battery on your lawnmower.

Locate and clean the battery of your mower prior to the testing. Use a flat-head screwdriver to clear any rust or debris from the top of the battery. This step ensures that the battery is correctly connected to the multimeter. Identify the kind of battery and the voltage it draws.

Tip: Ensure that your battery is sufficiently charged before testing it. If it has not been fully charged, it will can give an inaccurate reading.

● Step 2: Use the correct multimeter setting

Digital multimeters have a lot of setting you can use to measure different things. Use the DC voltage setting and use the setting that is closest to 12V but higher (for example, the 20 Volt setting). The exact setting will depend on your specific multimeter type.

● Step 3: Connect the multimeter to the battery.

Now that the multimeter is ready, you will have to connect it. Attach the two probes from the multimeter. Ensure that you use the correct ports on the multimeter. Attach the red probe to the + sign on the battery and the black probe against the – battery terminal.

● Step 4: Check and interpret the multimeter reading

When you connect the probes to the battery terminals, you will see a reading on a multimeter. This will tell the voltage of the battery and indicates the battery’s health.

If you measure a voltage around 12.6 Volt, it means that the battery is looking healthy. If you measure a higher voltage than 13 Volt, it is strange. It could mean that the battery is being charged, it is a different battery type, or there is something wrong with it. If you do not measure anything, or close to 0, the battery is dead. If you see a reading from 6 – 9 Volt, it means that the battery needs charging. A low voltage can mean that the battery condition is poor, but that is impossible to say at this time. The first step is to charge the battery. If you measure a low voltage after you have charged the battery, it means that it is in poor condition and needs to be replaced.

● Step 5: Measure again with a load attached

If the multimeter reading was close to 12.6 Volts, it means that the battery was charged and looks fine. But we have only checked it with no load. It is still possible that the reading is fine, but the battery is not in good shape. This is why we are going to test it again while it is being used.

The easiest way is to turn on the lights of the lawnmower. If your lawnmower does not have lights or another electrical attachment that you can use, you can use it to start the engine. If you can start the engine with no problems, the battery should be fine. If you notice that it has problems and is dead quickly, it means that the battery needs to be replaced.

If you have turned the lights or another attachment on, measure the voltage again. If you see a slightly lower voltage, it is fine. This is normal, as the battery is being used. If you see that the voltage is really lower, it means that the battery can not deliver enough power. In that case, you will need to replace it. You will probably see that the lights will have a reduced brightness, and starting the engine will be more difficult.

● Step 6: For some batteries, check the water level

If you have a battery where you can add water, check the current level. Remove the caps with a flat-headed screwdriver and add distilled water if needed. Note that more modern batteries are fully closed, and there is no need to check and add water to them.

Related Questions:

1. Can a lawnmower battery give you a shock?

No. The voltage of a lawnmower battery is too low. The only shock you could get from a lawnmower is from the voltage that is generated for the spark plug. This is a much higher voltage but will only be generated when the engine is running. A lawnmower battery can give sparks when you connect something or make a short. But usually, this will not be such that it can harm you.

2. Do I need to disconnect the battery before charging

No. There is no need to disconnect the battery before charging. You can connect the charger and leave the battery cables connected. If the battery is really dead, would we advise you to disconnect it and charge it separately.

3. My charger does not charge my battery

If your battery is dead, a modern charger will not charge it. It will give an error or turns itself off. Most modern chargers will not charge if they do not detect a certain minimum amount of energy. To make the battery charge again, you need to precharge it. This can be done with an older simple charger, or you can use another battery to charge it a little bit.

4. Why should you use a trickle charge with maintainer functionality?

Trickle charging a battery is a process where you keep the battery fully charged. When you store a battery, it will lose some of its charge over time. A modern charger with a trickle charger and maintainer functionality will measure the energy that the battery is losing and keep the battery fully charged and in an optimal state.

5. Is changing your lawnmower battery similar to changing your car battery?

Yes, changing your lawnmower battery is close to changing your car’s battery. If you know how to replace your car battery, it will be easy to replace your lawnmower’s battery and vice versa.

Final remarks:

A rechargeable lawnmower battery can be used effectively for at least three years. But it will slowly lose some of its capacity. You will notice this earlier when it is cold. At a certain time, you will need to replace the battery. Changing your lawnmower battery is relatively easy. Following the above steps if you do not have much experience with it. There is no need to hire a mechanic for this. Make sure you use the correct replacement battery.

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