It can be quite frustrating when the battery on your ATV won’t charge, either when it is installed on the bike or even when using an external battery charger. Or maybe it seems to be charging, but you can’t get it to hold a charge?

There are a few things you should look into before spending money on a new battery or other parts. If you’re lucky, you can fix the issue without even spending one single dollar.

Before you begin troubleshooting, it may be a good idea to read this post on how an ATV charges its battery.

Today’s post will cover these three different scenarios:

  • The battery is not charging when it is installed on the bike.
  • The battery will not take a charge, even when using an external charger.
  • The battery seems to be charging fine, but will not hold a charge over time.

At first sight, these scenarios seem very similar. But in most cases, they are actually quite different. While the problem that’s causing your issue may be the same in all three cases, often it is not.

Let’s dive into the actual troubleshooting.

Do you have a defect charging system or a bad battery?

It’s a good idea to begin your troubleshooting by identifying whether you have a faulty charging system on the ATV, or if the problem is with the battery itself.

The easiest way to do this is by trying to charge the battery using an external battery charger.

If the battery charges fine when using a charger, and holds its charge when sitting a few days under no load, you know that the problem is with the bike and not the battery.

If it does not charge or hold a charge when sitting disconnected, well then you know that the problem is with the battery.

bad atv battery wont charge
This battery has gone bad and cannot be charget to hold more than 4.25 volts.

Even if your battery is brand new and you are experiencing issues, I suggest that you follow these steps. Brand new batteries may be damaged as well.

Charge the battery using a battery charger

  • Put the key in the “Off” position.”
  • Locate your battery. It’s often located behind a plastic panel up high at the front of the ATV. But it may also be found on less ideal places, like on this Polaris Sportsman 570 where the battery sits exposed on the bottom of the frame. On some ATVs, it may even be at the rear of the bike.
battery location polaris sportsman 570
Can you spot the exposed battery?
  • Disconnect the battery terminals, so you know that nothing is drawing power from the battery.
  • Preferably remove the battery from the bike. There is always a small risk that something goes wrong when you charge a battery. If it were to start leaking or in worst case blow up, at least you won’t damage the ATV.
  • Connect a suitable battery charger and let it charge overnight — red cable to the positive terminal, black cable to the negative.

I prefer using fully automatic trickle chargers to keep the batteries on my vehicles healthy when not in use or when they need to be topped off.

ctek battery charger tender atv
The Ctek Multi XS 3600 is a cheap charger/tender that dos it’s job well.

This best selling Ctec has been with me for years and does its job very well. It will automatically shut off when the battery is full, or if there is a short or another issue inside the battery. Here you can find the lowest price on Amazon.

Read the battery voltage

When the charging cycle is complete, it’s time to read what voltage the battery holds. To do this, you will need a basic multimeter.

If you don’t have one, you can get them for cheap at your local auto parts store. Even the cheapest ones will do the job. Every home mechanic should have one, and I promise that you will find plenty of uses for it as soon as you learn the basics on how to use it.

  • Setup the multimeter to read DC voltage. The black cable should be in the COM port, and the red cable should be in the V DC port. Turn the dial to 20V DC. This setup should be used for voltage reading below 20 volts.
  • Put the test pin of the black cable to the negative lead on the battery. It should have a black protective cover and should be labeled “-.”
  • Put the test pin on the red cable to the battery’s positive lead. It should have a red protective cover and should be labeled “+.”
  • You should now read voltage in the multimeter display.
  • If the battery is healthy, you should be able to charge it so that it holds at least 12.4V (about 75% charged). If you can’t reach 12.4V, the battery is not taking charge properly.
  • Then let the battery sit for a day or two, and read the voltage once more. If the voltage has dropped well below 12.4V, you know that the battery is not holding a charge ant that there likely is an issue with the battery.

Now you should know whether you have an issue with the battery, or if the issue is with the charging system of the bike.

The battery won’t charge when using an external battery charger

Here are the most common causes when the battery won’t charge, even when using an external battery charger:

1. The battery is old or has gone bad

No battery lasts forever, and at some point, all batteries will stop working. If you take proper care of the battery, it should last for many years, but if you misuse it, you can ruin it in months or even days.

If you were not able to charge the battery above 12.4V, there is a good chance the battery has gone bad from misuse or just from being old.

There may be a bad cell with an internal short that is preventing the battery from taking a proper charge.

Another (and better) way of testing if the battery has gone bad is performing a so-called “Load test.” This simple test measure what charge the battery can maintain even under heavy load. You’ll find instructions on how to perform this test this post about what to do when a battery keeps draining for no apparent reason.

2. Low fluid levels in the battery

Acid lead batteries need a certain fluid level to take and hold a charge. The electrolytes should fully cover the plates inside of the battery.

If your battery is the Acid lead type and has covers that are meant to be opened, you can follow these simple steps to inspect and top of a battery that is low on battery acid.

Warning 1: Do not try to open a battery that is not designed to be opened. If fluid levels run low on a battery like this, there is nothing you can do but replace it with a new one.

Warning 2: Battery acid is highly corrosive and will cause permanent damage if it gets in contact with your skin or your eyes. Use proper eye protection and rubber gloves.

  • Use a rag and some ammonia-based window cleaner to clean the top of the battery. You do not want any debris falling into the battery when you open it. Let it dry completely before moving to the next step.
  • Use a screwdriver to pry open the caps, or unscrew them if they are threaded.
    Grab a flashlight and inspect each cell. The fluid should cover the plates inside the battery, and the fluid level should be about the same in each cell.
  • Top off any cells that are low on fluid. Use distilled water or store-bought battery water. Fill until you reach the maximum safe level, which is when the fluid is barely touching the bottom of the filler tubes.
  • Reinstall all of the caps.
  • Check for leaks. If the fluid levels were low in one or more cells, there might be a crack in the battery housing somewhere. If so, the battery needs to be replaced with a new one.
  • Attach a charger and check if it holds a charge now.

The ATV won’t charge the battery

In this scenario, the battery will charge just fine when you hook up an external charger, but it will not charge from running the ATV.

There are a few common causes you need to address.

1. The charging system is not working, bad stator

The charging system on an ATV is quite simple but nowhere near as efficient as the one you will find on a car. It uses a stator that produces a current inside of the engine when the engine is running. The output power from a stator is much less than what you get with an alternator, used on cars.

This is how the stator coil looks like.

The current then runs through a voltage regulator/rectifier that converts the current from three-phase AC voltage to DC voltage, as well as regulating the output current to 14V – 14.5V. This current is then what’s charging the battery, as well as powering all of the bikes electric components.

atv stator rotor
The stator and rotor is located inside the engine, behind this cover.

Even when the system works as intended, it may sometimes struggle to keep up to charge the battery to a full charge. This happens when you combine a low output charging system as the one you find on ATVs with using power-hungry accessories like a winch or heated grips.

You can test the stator by using a multimeter to measure resistance; the steps are described in this post.

Alternatively, you can measure what voltage output you get from the stator. This method is less accurate but will give you a good indication of whether the stator is working correctly or not.

The output voltage on a working ATV stator should be about 20V AC at idle to 40V AC or more when revving.

  • Unplug the three cable connector that goes from the stator.
atv stator connector
The plug has three pins that needs to be tested.
  • Set the multimeter to read AC voltage.
  • Start the bike while in “park”.
  • Insert the multimeter probes to the pins on the stator side of the connector. You will be combining all three pins as described below so that you can test all three phases.
    • Positive tester probe to pin 1 and negative tester probe to pin 2.
    • Positive tester probe to pin 1 and negative tester probe to pin 3.
    • Positive tester probe to pin 2 and negative tester probe to pin 3.
atv battery not charging stator
The voltage when idling 20V, witch is ok.

If any of the three phases did not put out 20V – 40V or more, the stator is likely not working correctly and needs to be replaced.

2. The charging system is not working, bad voltage regulator

If the stator checks out fine when doing the tests above, it’s time to see if the voltage regulator works as it should.

  • Locate the voltage regulator. Follow the three cables coming out from the stator. They should end up in a small aluminum box, usually (or ideally) located somewhere high on the bike where it won’t become soaked whenever riding in mud or water.
atv voltage regulator polaris
The voltage regulator on a Polaris Sportsman XP 1000.
  • With everything plugged back in, start the engine.
  • Use the multimeter to check the voltage that comes out of the regulator. There should be one red and one black cable. If there are no connectors readily available, press the point of the test pins so that it goes through the cable insulation to reach the cable wires inside.
  • The voltage output should be stable at 14V – 14.5V. If the voltage reading you get is far off, the regulator is likely bad and needs replacing.
  • Alternatively, the voltage may be jumping between 10V – 14.5V. This is also not good and usually means that the regulator has gone bad and needs to be replaced.

3. Loose or corroded wiring

ATVs are often used in wet conditions or bumpy off-road riding. This leaves the wiring particularly exposed to corrosion or coming loose.

A corroded or loose connection will prevent the battery from being properly charged.

Disconnect the battery connectors and clean them with some sandpaper before installing them again. The ground wire is particularly prone to corrosion.

Do the same with any exposed connectors found in the wiring from the stator and up to the battery.

The battery won’t hold a charge

In this final scenario we will cover what may be wrong when the battery seems to be charging just fine but then loses its charge after just a day or two, even when disconnected from the bike.

If you suspect that something other than the battery itself is causing it to drain, please refer to this post for proper troubleshooting for a battery that keeps going dead.

1. Low fluid levels

Even if the battery seems to be charging fine, there is a chance that fluid levels are low. Make sure all levels are correct as described above and recharge the battery to see if that helped.

2. The battery has become sulfated

Sulfation is a naturally occurring chemical reaction that’s happening inside of the battery when it’s being discharged. The process normally gets reversed when the battery is charged again.
Under certain circumstances, the sulfation becomes permanent and has damaged the battery.

This may happen when:

  • The battery acid level inside of the battery has been low for too long, leaving the plates exposed to air.
  • Completely discharging the battery – just a few days may be enough to inflict permanent damage.
  • The battery has been sitting for a long time with only a partial charge, either on the bike or in storage.

A sulfated battery loses a lot of its capacity and behaves as a small battery would. When you try to charge it, the charger will indicate that it is fully charged after just a short time of charging. But as soon as you disconnect the charger, the voltage will drop in just a matter of hours.

In some cases, it is possible to salvage a sulfated battery. But in most cases, the damage is beyond repair, and the battery needs replacing.

Try slow charging (trickle charging) the battery using a low amp charger for 24h for more. Sometimes, this may bring a dead battery back to life.

There are also chemical treatments available that may help you recondition a sulfated battery. But because ATV batteries are relatively cheap, I recommend that you rather get a new battery instead of spending time and money on a battery repair, that may or may not be successful.