So, will a lawn mower run with a dead battery? I know my push lawn mower doesn’t even have a battery and that works fine. But what about a gas lawn mower with a battery? Well, my riding lawn mower definitely has more wires and switches, so maybe this might help answer the question. So, let’s take a closer look at your lawn mower and see if it will run with a dead battery.
Will a Lawn Mower Run with a Dead Battery? (The Short Answer)
The battery on a lawn mower is responsible for several different jobs. This includes tasks like operating the starter motor and engaging the starter solenoid, the fuel solenoid, and the electric clutch. So, if your lawn mower battery is dead, then these tasks can not be completed, and your lawn mower will not run.
Confirming Your Battery is Indeed Dead
You’ll need to carry out two tests to confirm that your lawn mower battery is dead. The first is to test the battery without load. The second is to test the battery with load. The easiest way to do this is to use a battery tester.
So, when a 12v battery is charged, it should have a voltage reading of around 12.6v to 13v. Then when you test the battery under load, the voltage should drop to around 9.6v to 10.5v. So, even if your battery shows that it is fully charged without load but drops too low under load, it needs to be replaced.
People often make the mistake of just testing the battery without load using a multimeter and then looking elsewhere for a problem. So, disconnect your battery from your lawn mower and carry out these two tests.
Remember, the battery has to pass both tests to confirm if it’s dead or good.
The Role of a Lawn Mower Battery and Why a Mower Won’t Run if it’s Dead
As you have discovered, a battery on a lawn mower has several different tasks to undertake to both fire up your mower and keep it running. So, let’s take a closer look at these different tasks and see why a good battery is so important.
Starter Solenoid
The starter motor on your lawn mower requires a lot of power to crank over your mower’s engine. The power needed for this process is too much to run through the ignition switch. Therefore, your lawn mower uses a starter solenoid.
When you turn the key on your lawn mower, a small voltage is sent to the starter solenoid to activate its internal solenoid. As a result, the solenoid completes the connection between the battery and the starter motor momentarily while you hold the key in the start position.
Now, if you had a dead battery, you could use a jumper pack to get your lawn mower started up, as this process is only needed to start the lawn mower and not to keep it running.
Starter Motor
The starter motor is the device used to turn the lawn mower’s flywheel and set the coil in action. As a result, the flywheel turns and passes a magnet over the coil/s to generate the current needed to spark the spark plug.
So, if your battery is dead, this process is not going to happen, and your engine will not fire up. Again, you can jump your engine to bypass your dead battery, as this is only needed to start your lawn mower’s engine.
Fuel Cut-Off Solenoid
Nearly all lawn mowers with electric starting systems have a fuel cut-off solenoid. This small solenoid sits at the bottom of the carburetor and switches the fuel on and off. When the solenoid is powered, the fuel is on, and when the solenoid has no power, the fuel is cut-off.
So, even if you jumped your lawn mower to start the engine, it would soon die because there would be no power for the fuel-cut-off solenoid to allow fuel to flow to the engine. But if you have a battery that will hold a charge but has a problem under load and you jumped your lawn mower, you might find that your fuel cut-off solenoid will still have enough power to remain open.
This means you might actually be able to keep your lawn mower running. But in my experience, this doesn’t really happen too often.
Blade Electromagnetic Clutch
Next on the list is the blade clutch. So, the drive shaft that comes out of the bottom of the engine serves two purposes. One to run the drive and the other to run the blades. Now, a blade clutch is used so that you can engage and disengage the blades when you need to.
Not all lawn mowers have these types of clutches, but most modern lawn tractors and zero-turn lawn mowers do. Some lawn mowers might use a manual belt tensioner to engage the blades or a spinning disc to engage the drive, but bigger lawn mowers are increasingly turning to electromagnetic clutches. Therefore, to engage your lawn mower blades, you are going to need a good battery to activate the electromagnet inside the clutch.
So, even if you managed to jump your lawn mower and the battery has just enough power to keep the fuel cut-off solenoid open, the activating of the clutch will probably draw too much power, and your lawn mower will stall very quickly.
The Rest of the Electrical System
Now that we have looked at the big items that need a good battery to function let’s see what else might need to draw some power. Depending on your lawn mower, you might have things like lights, gauges, and engine hour clocks. All of these things are going to need power.
Also, you will definitely have safety systems drawing power to keep your lawn mower running. Safety switches under the seat, roll bars, and blades all need power. So, will a lawn mower run with a dead battery? Well, jumping your lawn mower might work for a moment, but I’m pretty sure it won’t last very long.
Your Options If Your Mower’s Battery Is Dead
Whenever my lawn mower battery is dead, I check a few things first before I run to the store to buy a new battery. If I left the lights or the ignition switched on, then the battery is just flat. This doesn’t mean it’s done for; it just means it needs some attention. So, here is my process.
- Charge the Battery
- Test the Battery
- Use the Battery
- Re-Test the Battery
- Look for a Different Problem
Charge the Battery
The first step I carry out is to charge the battery fully. I always like to remove the battery from the lawn mower and charge it up on my workbench. Now, you don’t need to do this because you can charge a battery while it’s connected, but if there is an electrical fault on your lawn mower, you might have a problem charging.
This could give you a false result when charging, and you might think it’s the battery at fault. So, disconnect the battery, connect your battery charger, then wait for the battery to charge fully.
Test the Battery
Once my battery is fully charged, I then grab my tester and carry out the two tests from before. First, I test the battery with load and without load. If the readings are good, then I’ll reinstall the battery on my lawn mower. If the results are bad, then I’ll have to get myself to the lawn mower store for a new battery.
So, if my lawn mower stopped working between cuts and the battery charged up ok, then I probably left the lights on, or the ignition switched on. Keep in mind that batteries will naturally go flat over time or during cold weather. If your battery is flat at the start of the cutting season, then these two reasons are probably the cause.
Use the Battery
The next step is to use my lawn mower and see how the battery reacts. If I don’t have any other problems, then this confirms that the battery was, in fact, flat. So, either I left something switched on, or it could be down to the fact the lawn mower hasn’t been used in a while, and it got cold.
If you have a lawn mower stored over winter, then freezing temperatures can drain a battery 30-60%. So, I’d expect the battery left over winter to be flat unless it was connected to a trickle charger.
Recharge & Re-Test the Battery
If I have some problems with my lawn mower and I still think it’s battery related, then I recharge and re-test the battery. If I get a good reading once I fully recharge the battery, then I need to look for a problem elsewhere.
For this, I want to figure out if the battery is either going flat while I’m using the lawn mower or when it’s not being used. This would tell me if there is a problem with a component of the lawn mower draining the battery or a problem with the lawn mower not being able to charge the battery correctly.
Look for a Different Problem
What drains a battery when your lawn mower isn’t being used? Well, lights, an ignition, or even a faulty relay can be the problem. But if I had to look somewhere first, it would be at the charging system on the lawn mower: the stator.
This device works pretty much the same as an ignition coil, but instead of sending a charge to the spark plug, the stator sends a charge to the battery to recharge. If you pull off the flywheel on your lawn mower, you’ll find your lawn mower’s stator.
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