A lawn tractor’s battery lasts about three years, so if you keep it for longer, you’ll need to replace it at some point. Now, the last time I had to replace my lawn mower battery, my mower wouldn’t start with the new battery. It was kind of confusing because all I did was swap out the battery. So, if you are having trouble and your lawn mower won’t turn over with a new battery, let me share with you what I did to get my mower up and running again.
Why Might a Lawn Mower Not Start with a New Battery? (The Short Answer)
When you turn the key on a lawn mower, you should hear the starter solenoid click as it engages. If you don’t hear this click, then there could be a problem with the connection between the battery and the starter solenoid. Usually, this is caused by a loose or poor connection at the battery posts.
Diagnosing Why Your Lawn Mower Won’t Turn Over with a New Battery
So, to diagnose why your lawn mower won’t turn over with a new battery, you’re going to want to carry out a couple of tests. These tests will determine if there is a problem with the new battery or with the new connection.
Test the New Battery with a Battery Tester
Before I start to look at the lawn mower for a problem, I always begin by testing the new battery. There might be a chance that your lawn mower won’t turn over with a new battery because there’s actually an issue with the new battery.
So, I use a 12v/6v DC selectable battery tester that I picked up at Harbor Freight for $20 to test my battery. This kind of tester allows you to test the battery at rest and when it’s under load. Just because a battery has volts doesn’t mean it has enough power to turn over the mower when it’s under load.
Connect the tester and check the voltage. Usually, testers have a gauge that tells you if the battery is good or bad. Then, turn the ignition key and watch what the gauge does. If the needle gauge drops to bad/low, then you’ll know there’s a problem with the new battery.
If the gauge doesn’t even flicker, then you know there is a problem elsewhere. If the tester flickers and stays in the good range on the tester, then the engine will likely start. But I’m guessing this isn’t going to happen with your lawn mower.
Test the New Battery with a Charger
Before you head to the store, get a battery tester and check to see if your battery charger has a testing function. If it does, then you can use it to check that the battery is fully charged.
Also, if you have one of these new smart chargers, it might also be able to check the battery under load. If you do, then you can just use your charge to tell you the condition of the new battery.
Try Starting the Mower With a Starter Pack
If you have a starter pack, then there is another test you can do which will tell you if there is a problem with the battery. If you connect a jumper pack to the battery posts and set the pack to engine start mode, you can try to crank the engine. If it starts, then you’ll know that the problem lies with the battery and the connections.
Test the Voltage Reaching the Starter Solenoid
By this point, you will have diagnosed whether the battery is, in fact, good and that your lawn mower will actually start. So, with a good battery and a mower that will start, the last thing to check is the connections at the battery posts.
Set your multimeter to 20v DC, then connect the positive side input to the starter solenoid and the negative to the mower’s frame. Just make sure that you are connecting the negative side to bare metal so that you get a good ground connection.
Alternatively, you can connect the negative side of the multimeter to the negative post on the battery. Now, take a look at the reading on your metal. I’m pretty sure you’re either going to get no reading or a very low reading.
Check the Battery Post for Corrosion
Ok, so this is where I discovered why my riding lawn mower won’t start with a new battery. If you take a close look at the battery terminals, you’ll probably find some corrosion that is preventing a good connection between the battery and the electrical system.
In my case, the battery is under the seat of the mower, and it can get pretty wet under there, either from rain or when I wash down my mower. I was actually surprised at how dirty and corroded my terminals were.
Check that the Battery Terminal is Fastened Tightly
Now with all the corrosion, I noticed that the bolts holding the cable to the battery weren’t really doing a very good job. When I wiggled the cables, there would be some movement. So, wiggle your cables and check if they’re loose. If they can move, then you could have found the reason your lawn mower won’t turn over with a new battery.
Fixing a Riding Mower that Won’t Start with a New Battery (4 Things to Try)
If you tested your new battery and it was bad, then I recommend that you return it to the store you purchased it from. They’ll probably just swap it out or give you a replacement. I don’t suggest you try to charge it because there could be an underlying issue that could cause problems further down the line.
So, if your battery is good and you are still having problems, then let’s take a look at a couple of fixes I’ve used in the past to get my mower working again.
Clean the Battery Posts
First of all, remove the cables from your battery and set them out of the way. Then use a wire brush to clean the posts, including the holes through the posts. Now, your terminals should be in pretty good condition as the battery is new, but anything that was on the cable terminals could now be on the battery posts.
If you want to do a really good job cleaning the posts, then you should head to a car parts store, like AutoZone or Advanced Auto Parts, and pick up a post-cleaning brush. It’s a round wire brush that fits over the post and makes quick work of cleaning. It saves you from scuffing up your new battery with a regular wire brush.
Clean the Cable Terminals
Next, clean the terminals on the end of the positive and negative cables coming from the lawn mower. This is where I found most of the corrosion causing my lawn mower not to start. So, take a wire brush and give all the contact points a good cleaning. You’ll want to make sure you remove all the corrosion and dirt from the terminal.
Replace the Terminal/Post Nuts & Bolts
So, the nuts on my battery were actually pretty worn down and rusty. This was partly because they were a bit loose but also because they were made of regular steel. Now, you could clean your original nuts and bolts, but I just replaced mine with a set of stainless steel nuts and bolts. No more rust.
Also, if you have nuts that are wing nuts, then I definitely recommend ditching them and getting some proper nuts. It’s difficult to get a nice, tight fitting with wing nuts.
Protect the Terminals
After all my diagnosing and testing, the reason my lawn mower won’t turn over with a new battery came down to a bad connection between the battery posts and the cable connectors. This was due to a mixture of corrosion and loose cables.
So, once you have cleaned the terminals and replaced the fixings, you should be able to fire up your mower and get back to cutting. But it’s only going to be a matter of time before this problem raises its head again.
Batteries on lawn mowers are not protected all that well from the elements like they are on cars. So, you can take an extra step and use battery terminal grease. Terminal grease prevents corrosion and insulates the connection from dirt and water.
You can grab a pack of terminal grease from the auto store for less than $2, which will prevent this issue from popping up too quickly in the future.