What keeps draining my lawn mower battery?

Approx Reading Time: 10 minutes

If you have a lawnmower with an electric starter, it needs to have a battery to make it crank the engine. In almost all the models, it will be a lead-acid battery that can also power the lights if available. Now, suppose your lawnmower doesn’t start as you turn your key in the ignition switch. Well, one of the reasons could be a drained battery. A lawn mower’s battery usually recharges while the mower is busy trimming the grass. However, suppose the battery is already drained every time you try to start the lawnmower? In that case, it may be caused due to one of several possible reasons. In this blog post, we will look into the reasons and fixes.

What keeps draining my lawnmower battery:

  • More power usage than the lawn mower’s electrical system capacity
  • Parasitic electrical drain
  • Corroded battery posts
  • Voltage regulator problem

Additional Voltage regulator test to determine additional causes of battery drainage:

  • Perform a voltage test on the voltage regulator.
  • Perform a voltage test on the lawn mower’s stator.

The function of a battery in a lawnmower:

The battery performs two prime roles in the lawnmower:

  1. Starting the lawnmower: To provide the requisite electrical power needed to start the lawnmower.
  2. Power other equipment: To provide a reference point (ground) for the lawn mower’s electrical system controlling almost all the electrical equipment.

Suppose the lawn mower’s electrical system and the battery both are in perfect condition. In that case, the battery shall provide the initial start-up power to the lawn mower’s engine, and the engine is running, it shall charge the battery simultaneously. But a snag in either of the two causes battery drainage.

We shall provide an in-depth analysis of the reasons that can cause battery drainage. What kind of tools do you need to test it and find the leading cause of drainage.

Causes of Lawnmower Battery Drainage:

● Reason 1: More power usage than lawn mower’s electrical system capacity

Some lawn mowers are created to be used as lawn tractors or small snowplows. While performing these tasks, one usually needs to use trailer lighting, headlamps, or other extra functionalities.  

Suppose the lawn mower’s engine merely produces the energy required to charge the battery. In that case, these different devices suck the power that was to be used to charge the battery.

– Fix: Using less power

If that’s the case, all the lawnmower equipment that performs extra unnecessary functionalities must be turned off during the lawn mower’s operation. This step is done so that the battery may receive the full power required to revive itself. If turning off is not possible, you could leave the mower running for some time after you finished with all the appliances turned off to recharge the battery.

● Reason 2: Parasitic electrical drain

Electrical System: The lawn mower’s electrical system may drain the battery while the lawnmower is turned off. The electrical system may resume drawing current from the battery due to an unwanted connection in the system. This connection can be due to parts touching each other, moisture, or other reasons.

– Relay equipment turned on:

The drain may also be caused because some electrical relay equipment remains turned on even if the lawnmower is switched off. These devices obviously, draw unnecessary electric current and rob the battery. Some equipment has a standby mode that uses power.

– Test for an unnecessary current draw:

To check whether current is being drawn from the battery while the lawnmower is turned off, we need to perform a test using a multimeter by following the following mini procedure with steps:

  • Step 1: Set the multimeter to ammeter mode.
  • Step 2: Place the multimeter’s positive terminal on the battery’s positive terminal and its negative end to the battery’s negative.
  • Step 3: Suppose the ammeter shows a value greater than 1mA. In that case, it means that the electrical system is drawing power from the battery while the lawnmower is off.

– Use the multimeter resistance mode:

Finding the cause of parasitic electrical drains can be really hard. Another method to find the reason is by using the resistance mode on a multimeter. Disconnect the battery, turn off all appliances, and remove as much as possible. Then measure the resistance between the two battery connectors. Reattach the appliances (still turned off) and check if you can see a difference in resistance. Also, check that moisture is not the cause. You can do that by parking the lawnmower in a dry location and check after some time.

● Reason 3: Corroded battery posts:

Another possible reason for battery drainage is corroded battery posts. There might also form a white, crusty powder around the battery’s terminals. This causes the battery to put in extra effort, which causes the battery to drain faster. So, the battery posts and terminals should be cleaned regularly with a clean cloth. Also, loose connections of battery terminals to battery posts may cause battery drainage, so don’t forget to tighten them regularly.

● Reason 4: Voltage regulator problem

A voltage regulator’s function in a lawnmower is to convert the engine’s voltage into the correct voltage and then supply it to the battery to charge it.

However, the voltage regulator may also be one of the causes of the lawn mower’s battery drainage. It may continue to draw current from the battery even after the lawnmower is shut down.

– Test to check if the voltage regulator is draining the battery:

To test if the voltage regulator is robbing the battery, you need to perform a test using a multimeter.

  • Step 1: Set the multimeter to ammeter mode and place the multimeter’s positive terminal on the voltage regulator’s positive end. Then, touch the multimeter’s negative terminal to the lawnmower’s metallic body.
  • Step 2: If the ammeter shows a value of above 10mA, your voltage regulator is drawing current from the battery, causing it to drain and is short-circuited from inside.
  • Step 3: The voltage regulator needs to be replaced by a new one in this case. Remember to buy the same model voltage regulator as the one being replaced.

● Test 1: Perform a voltage test on the voltage regulator

When a lawnmower starts, the flywheel located inside the lawn mower’s engine also starts its rotation. This flywheel is nothing but an alternator that has magnets that create an A.C. voltage of about 30V. This A.C. voltage is fed into a voltage regulator that converts this 30V A.C. into about 15V D.C., which is then provided to the battery for the charging purpose. One of the causes that result in battery drainage is that the voltage regulator might not be supplying enough voltage back to the battery. To verify if this is the reason, we need to perform a test on the voltage regulator.

– Testing procedure:

  • Step 1: Set your multimeter to D.C. voltage measurement mode.
  • Step 2: Turn the key switch to on position.
  • Step 3: Remove the wire’s connection that supplies voltage to the battery. Place the positive terminal of the multimeter on the voltage regulator’s positive. And place the multimeter’s negative on the lawnmower’s metallic body.
  • Step 4: The multimeter should display a value of about 12V, indicating that the voltage regulator supplies voltage back to the battery.
  • Step 5: But suppose the multimeter shows very low or no voltage value. In that case, there is an issue with the voltage regulator. Hence, it needs to be replaced by a new one.

● Test 2: Perform a voltage test on the lawn mower’s stator:

The lawnmower stator supplies A.C. voltage to the voltage regulator, which then provides juice to the battery to charge up. But in some cases, the lawnmower stator may not be supplying sufficient A.C. voltage to the voltage regulator, which may be one of the possible causes of battery drainage. To verify if this is the issue, we need to perform a test on the stator using a multimeter.

– Testing procedure:

  • Step 1: Set your multimeter to A.C. voltage measurement mode.
  • Step 2: Start the lawnmower.
  • Step 3: Remove the connection of the wire coming out of the stator from the voltage regulator.
  • Step 4: Insert the multimeter’s terminals inside the stator wire’s terminals.
  • Step 5: The multimeter should display a reading of about 30V. If the multimeter shows a reading below 20V, then the stator needs to be replaced by a new one.

Related Questions:

1) How can I check if my lawnmower’s battery is dead?

When the lawnmower hasn’t been used for a year or more, there is a high probability that the lawnmower’s battery won’t have any juice left and maybe dead. To check that, we can perform a simple test on the battery using a voltmeter. The steps are as mentioned below:

  • Step 1: Firstly, you need to charge the battery to its full capacity.
  • Step 2: Now, take a multimeter and set it to D.C. voltage measurement mode.
  • Step 3: Place the multimeter’s positive terminal on the battery’s positive terminal and multimeter’s negative to the battery’s negative.
  • Step 4: The multimeter would show a reading of about 12V.
  • Step 5: Next, leave the battery for about 30 minutes, and then again measure the voltage across the battery using a multimeter.
  • Step 6: Suppose the reading shown by my multimeter drops to about 5V or less or is decreasing continuously. In that case, it means that the battery is no longer functional and needs to be replaced by a new one.
  • Step 7: While installing the new battery, please check if the battery is a regular terminal or reverse terminal and make connections regularly.

2) How to store a lawnmower battery for winter?

  • Remove the battery: Usually, lawnmowers aren’t used during the winter season and are held in garages. Most lawnmower owners make one common mistake because they do not remove the lawnmower’s battery before storing it for the winter season. This may cause your battery to die, and so, your lawnmower won’t start the next time you want to put it to use. So, it is necessary to extract the battery before putting the lawnmower away for winter or an extended period.
  • Clean the battery: The battery must be cleaned using a dry rag and baking soda charged entirely with a battery charger and stored in a separate dry place in a cardboard box. This will, for sure, maximize the battery’s life.

Final Remarks:

The battery is a crucial part of a lawnmower, and the lawnmower would be useless to you if the battery drains repeatedly. Therefore, you must find the cause of battery drainage by taking help from this article and remove that problem immediately so that you can make your lawn blooming and more beautiful. The battery must be maintained b regularly filling it with distilled water and recharging it. The battery shall also be cleaned time and again to prevent corrosion and prolong its life. Finally, don’t forget to perform timely maintenance of the lawnmower’s other parts such as filters, cutting blades, and oil.