Dead Lawn Mower Battery?

Lawn Mower Battery

Why do I have a dead lawnmower battery? Sound familiar? One of the most frustrating things about owning a lawnmower is when your ready to use it, it won’t start! Whether is due to a dead battery (which we will cover in this article) or some other irritant. There is one thing to count on and that is, one day it will fail you. Equipment is kind of like people, at some point they will fail you but that doesn’t mean it’s time to discard them, maybe it just time to give them a little love and understanding.

If your reading this article I would assume your having a dead battery issue so I’m hoping Fixits will help shed some light on the situation. We will cover everything from how to test your battery, testing the charging system and everything in between. With a few simple tests you can correct the dead battery issue once and for all on your lawnmower. So whether its a new Spartan Zero Turn that we offer at Fixits Outdoor Power or a xyz brand, this article should prove to be helpful.

Tools Needed

  • Multi-meter
  • Battery Load Tester
  • Hand Tools to remove battery

Test your Battery

Even if you are convinced the battery is charged and good, test it anyway. After all your questions is why do I have a dead lawnmower battery? Do not skip this step. Many have wasted lots of time and money by assuming the battery itself isn’t the issue. The only correct way to test your battery is to use a load tester when the battery is fully charged. In a pinch you can mimic a load on the battery by trying to start the engine and reading voltage drop with your meter. One thing to note is that the battery needs to be fully charged in order to accurately perform either test. To test it without a load tester, simply hook your voltage meter up to the battery, try to start the mower and watch how far the voltage drops from the static reading. If it drops below 9.5 volts something is up. Unfortunately this test isn’t full proof because bad connections and poor grounds will cause the exact same voltage drop issue. This is a common reason as to why your lawnmower battery keeps going dead. The best way is to actually remove the battery and do a isolated load test with battery load tester or take it somewhere to be tested. Don’t forget it needs to have a full charge in order to properly get the results your looking for. After confirming your battery is good or replacing it with a known good battery move to the next step.

Test your connections to correct your lawnmower battery from going dead.

Put your meter on DC voltage and connect the negative lead to ground and the positive lead to the charge wire on your regulator/rectifier. Generally speaking this will be mounted on the side of your engine. After you locate your regulator you’ll notice three wires. Most of the time two of the wires are yellow or white, those are your wires coming from your stator and the other wire is generally red. The red one is the one you will need to hook to your positive lead. Most red/charge wire’s on Kawasaki and Kohler engines is the center wire on the regulator however sometimes not, just be sure you know which is what. Briggs generally have yellow and red wires. Record what the voltage is on this connection and compare it to the reading on your battery. They should be the same. If you get no voltage at the regulator your charge wire is not connected either because your fuse is blown or a broken or loose connection. Replace the fuse or correct connections before moving forward otherwise you’ll keep asking yourself, “why do I have a dead lawnmower battery? If the voltage at the regulator is lower than the battery voltage clean all your connections and firm up any grounds. After you’ve determined that the voltage on the regulator is the same its time to move to the next step.

Test your charging system to determine why your lawnmower battery keeps going dead.

  1. Take a static reading of your battery voltage. (voltage at the battery without the engine running) and record it.
  2. Start your engine and measure the voltage on the battery again while your throttle is running at top rpm. If the charging system is working properly working, the voltage while at top rpm on the battery will be quite a bit higher than the static reading you recorded earlier. A good reading will be north of 13 volts. If you find voltage is the same, barley higher or lower than the static reading this tells you the charging system isn’t working properly and further tests need to be performed in order to determine why your lawnmower battery keeps going dead. Taking your time properly testing can help you figure out why your lawnmower battery is going dead. You’ve determined the connections and battery are all good at this point so that only leaves a faulty stator or the voltage regulator or a bad ground to your regulator. Check ground using ohms on your meter before moving forward. So at this point you will need to test the stator in order to determine if its the stator or the regulator is causing the issue.

What is a stator and what is the difference between it and the regulator/rectifier you ask? And how do I test it?

In the most simplest forms a stator comprises of copper windings mounted under your flywheel that works in conjunction with magnets to produce AC voltage. This AC voltage is sent to the regulator/rectifier to changed into DC voltage. If either component is faulty, it would explain why your lawnmower battery keeps going dead.

  1. Test your stator by un-hooking the three connections to the regulator. Turn your meter to AC volts, start your engine, run rpm’s all the way up and take note of the reading. Spec’s and voltage for each stator type will vary but generally speaking you should have 28-38 AC volts. Lower than 28 or 40 or higher means you should replace the stator.
  2. If the stator is testing within range go ahead and hook the three wires back up and turn your meter back to DC volts. Start your engine again and run rpms all the way up. Then test the red/charge wire while its hooked up. If you do not get 13.5-14 volts dc then replace your regulator.


  • Battery wont take a charge or hold under load
  • Faulty regulator
  • faulty stator
  • Bad connections

Common symptoms and cause of a low voltage issues

  • After cutting with the mower and suddenly the mower dies. (Battery is likely not charging)
  • Mower just clicks when you turn the key. (Bad connection or weak battery)
  • Mower worked fine and then it sat for a extended period of time and is now dead? (Bad battery)
  • Everything seems to work fine but sometimes when you try and start it, the engine just barley wants to turn over and then it goes ahead and starts. (mis-adjusted valves) Blog soon to come on adjusting valve lash.

Lets wrap it up!

Thank you for taking time to read the article and if you are in need of service work on any make or model of outdoor power equipment in the Oklahoma City and surrounding area be sure to look us up at Fixits Outdoor Power. We also offer parts, sales, and service on all power sports equipment (utv’s atv’c, golf carts etc…) at our sister company Funky Monkey Power Sports where we offer new, used and excellent service right here in Canadian County.

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