Milwaukee M12 Battery Not Charging: How to Fix?

Milwaukee M12 Battery Not Charging: How to Fix?

The Milwaukee M12 Battery Not Charging is a common issue faced by users of the Milwaukee brand. This problem can be frustrating and disruptive, especially if you rely on your tools for work or projects. However, there are steps you can take to fix this issue and get your batteries charging again.

What Is Milwaukee M12 Battery?

Before we dive into the solution for fixing a Milwaukee M12 Battery not charging, it’s important to first understand what exactly this battery is. The Milwaukee M12 Battery is a rechargeable lithium-ion battery used in various Milwaukee power tools. It comes in different voltages, with the most common being 12 volts.

What Is Milwaukee M12 Battery?

Milwaukee is a reputable brand known for its high-quality and durable power tools, and their M12 battery is no exception. It provides reliable and long-lasting power for your tools, making it a popular choice among professionals and DIY enthusiasts alike. [2]

Reasons Why The Milwaukee M12 Battery Won’t Charge

Now that we have a basic understanding of the Milwaukee M12 Battery, let’s explore some common reasons why it may not be charging:

  • Battery Overheating: One of the most common reasons for a Milwaukee M12 Battery not charging is overheating. This can happen when the battery is exposed to extreme temperatures or has been used continuously for an extended period.
  • Dirt and Debris: Another common culprit for a non-charging battery is dirt and debris. If the battery contacts or charging ports are dirty, it can prevent proper connection and hinder the charging process.
  • Damaged Battery Cells: Over time, the cells in a lithium-ion battery may become damaged, resulting in decreased performance and difficulty holding a charge. [2]

Makita m12 Battery Terminals

First Terminal

The first terminal is the Positive (+) terminal and is usually marked with a plus sign. This is where the power flows from the battery to your tool, giving it the energy needed to function. [2]

Second Terminal

The second terminal is the Negative (-) terminal, typically marked with a minus sign. It serves as the return path for the electrical current when the tool is in use. [2]

Three Hidden Terminals

Some Milwaukee M12 batteries also have three hidden terminals, which are not visible when looking at the battery. These terminals are used for communication between the battery and the charger, ensuring proper charging and extending the battery’s lifespan. [2]

Fifth Terminal

The fifth terminal, often referred to as the thermistor, is a safety feature that monitors the battery’s temperature during charging. If the battery gets too hot or cold, it will prevent it from charging to protect against potential hazards. [2]

Makita m12 Battery Terminals

How To Charge A Milwaukee M12 Battery?

Now that we know the different terminals of the Milwaukee M12 battery, let’s discuss how to properly charge it:

  1. Use a Compatible Charger: It is essential to use a charger specifically designed for Milwaukee M12 batteries. Using an incompatible charger can damage the battery and hinder its performance.
  2. Clean Battery and Charging Port: Before charging, make sure the battery contacts and charging ports are clean. Use a dry cloth to remove any dirt or debris that may be preventing proper contact.
  3. Insert the Battery: Insert the battery into the charger, making sure it is securely connected to both terminals.
  4. Check for Blinking Lights: Most Milwaukee chargers have blinking lights that indicate the charging status. A steady red light means the battery is charging, while a green light indicates it is fully charged.
  5. Allow Sufficient Charging Time: It can take anywhere from 30 minutes to an hour for a Milwaukee M12 battery to fully charge, depending on its current level and the charger’s output.
  6. Disconnect When Fully Charged: Once the battery is fully charged, disconnect it from the charger and remove it from the charging port. [3]

Check The Charger With A Multimeter First

If you’ve followed the steps above and your Milwaukee M12 battery is still not charging, it may be time to check the charger with a multimeter. A multimeter is a handy tool that measures voltage, current, resistance, and continuity.

  1. Set Multimeter to DC Voltage: Set your multimeter to measure DC voltage and adjust the range to at least 20 volts.
  2. Connect the Test Leads: Connect the black lead of the multimeter to the negative (-) terminal and the red lead to the positive (+) terminal of your charger.
  3. Check for Voltage Reading: Turn on your multimeter and check for a voltage reading. If you see a reading between 12-18 volts, it means your charger is functioning correctly.
  4. No Voltage Reading: If there is no voltage reading or a reading below 12 volts, it could indicate an issue with your charger and further troubleshooting may be needed. [3]

Clean Off The Terminals On The Battery

If the charger is functioning correctly and you’re still experiencing issues, the problem might be related to your battery. In such cases, it’s recommended to clean off the terminals on the battery with a dry cloth. This will help remove any dirt or debris that may be hindering proper contact and causing the problem. However, if this doesn’t resolve the issue, it could indicate a more serious problem, such as a damaged battery, which might require replacement. It’s always best to consult a professional in such situations for further assistance and guidance. [3]

Clean Off The Terminals On The Battery

Check That There Is Power Coming Out Of The Charger

Another potential issue that could prevent the battery from charging is a lack of power output from the charger. This can occur when the charger fails to supply sufficient power to the battery. To determine if your charger is indeed outputting the required power, you can employ the use of a multimeter, as explained in the previous section. Additionally, you can also try using the charger with another compatible battery to observe if it charges properly under those circumstances. If, after conducting these tests, you find that there is no power being emitted by the charger, it is likely that the charger will need to be replaced with a new one. [3]

Hold The Power Button

Some users have reported that holding down the power button on their Milwaukee M12 tools for a few seconds, until the LED indicator flashes, has helped resolve charging issues. This can work as a temporary solution, providing a quick fix for the problem at hand. However, it is important to note that this method is not recommended as a long-term fix, as it may not address the underlying cause of the issue. If you find yourself needing to hold down the power button every time you charge your battery, it could indicate a more complex problem that requires further attention and troubleshooting. It is advisable to consult the manufacturer’s guidelines or seek assistance from a professional to ensure proper resolution and avoid potential damage to your tools. [3]

Troubleshoot Your Cable, Charger, Outlet & Case

Before jumping to the conclusion that your battery or charger is faulty, it’s crucial to thoroughly investigate and rule out any other potential causes for the problem. Start by carefully examining the cable and charging port, looking for any signs of damage or debris that could be obstructing proper contact. Additionally, try plugging your charger into a different outlet or using a different charging case to determine if the issue persists. If, despite these efforts, the problem still persists, it may indicate a malfunction with either the battery or charger. In such cases, further troubleshooting or even replacement might be necessary to resolve the issue effectively. [1]

Troubleshoot Your Battery Charge Indicator

If your Milwaukee M12 battery is not charging, it could be due to a faulty battery charge indicator. This indicator is responsible for accurately displaying the battery’s charging status. To troubleshoot this issue, you can try charging the battery until it reaches full capacity and then using it until it fully discharges. By repeating this process a few times, you can assess the battery’s performance and take note of how long it lasts before needing to be charged again.

During this evaluation, it’s important to pay close attention to any significant decrease in battery life. If you observe a noticeable decline in the battery’s overall runtime, it could indicate a problem with the charge indicator. In such cases, it is recommended to seek professional assistance for repair or replacement of the battery.

Alternatively, you can also attempt to reset the battery by fully charging it and then completely discharging it three times consecutively. This process may help recalibrate the charge indicator and restore proper functionality.

Remember, proper care and maintenance are essential for your Milwaukee M12 battery’s longevity and optimal performance. [1]

Troubleshoot Your Battery Charge Indicator

Troubleshoot Your Screen & Battery

Lastly, if you’re still facing charging issues with your Milwaukee M12 battery, it’s important to thoroughly inspect the screen on both the charger and battery. Take a close look for any signs of physical damage, such as cracks or dents, as well as any visible malfunctions that could potentially impact the charging process. Additionally, pay attention to any abnormalities like flickering lights or error messages on the charger or battery screen.

If you do happen to notice any of these issues, it’s highly recommended to seek professional guidance. Reach out to a knowledgeable technician who can provide further assistance and advise you on potential repair or replacement options. Taking the necessary steps to address these concerns promptly will help ensure optimal performance and longevity of your battery. [1]

Consider Replacing The Battery

In some cases, the issue may persist even after trying various troubleshooting methods. This could indicate a more severe problem with either the battery or charger that cannot be resolved through simple fixes. In such situations, it’s best to consider replacing your Milwaukee M12 battery with a new one. This will not only resolve the charging issue but also provide you with a reliable and long-lasting power source for your tools. Additionally, it’s important to properly dispose of your old battery according to the manufacturer’s guidelines to ensure safety and proper handling of the device. Overall, taking proper care of your battery and promptly addressing any charging issues will help prolong its lifespan and keep your Milwaukee M12 tools running at their best. [4]

Advantages Of Milwaukee M12 Battery

Now that you know how to troubleshoot and resolve charging issues with your Milwaukee M12 battery, it’s important to understand the advantages of using this particular brand and model. The Milwaukee M12 battery offers a compact and lightweight design, making it easy to handle and transport when working on various projects. It also provides longer run time compared to other batteries in its class, allowing you to work for longer periods without interruption. Additionally, the M12 battery has a built-in overload protection system that helps prevent overheating and prolongs its lifespan. With these benefits in mind, it’s no wonder why Milwaukee M12 batteries are a popular choice among professionals and DIY enthusiasts alike. [4]

Disadvantages Of Milwaukee M12 Battery

While the Milwaukee M12 battery offers many advantages, it’s important to note that there are also some potential drawbacks to consider. One of the main disadvantages is its compatibility with only specific tools within the Milwaukee M12 line. This means that if you have tools from other brands or models, you may not be able to use the M12 battery interchangeably. Additionally, the M12 battery has a smaller capacity compared to larger batteries, which may not be suitable for heavy-duty or prolonged use. Lastly, the cost of purchasing and replacing Milwaukee M12 batteries may be higher compared to other brands. Before investing in this battery, it’s important to do your research and consider your specific needs to determine if it’s the right choice for you. [4]

Safety Precaution When Handling Batteries

Lastly, it’s important to mention some safety precautions to keep in mind when handling and using any type of battery. It is essential to always follow the manufacturer’s guidelines and instructions for charging, storing, and disposing of batteries safely. Never attempt to modify or alter a battery in any way, as this can lead to potential hazards. Similarly, never mix different types or brands of batteries, as this can also pose safety risks. If at any point you notice a battery behaving abnormally or exhibiting any signs of damage, stop using it immediately and seek professional assistance. Remember to always prioritize your safety and the proper handling of batteries for optimal performance and longevity. [4]

Safety Precaution When Handling Batteries


How do I reset my Milwaukee battery?

To reset your Milwaukee battery, start by fully charging it and then completely discharging it three times in a row. This will help calibrate the battery and potentially resolve any charging issues.

Why is my m12 battery blinking red?

A blinking red light on your Milwaukee M12 battery could indicate a faulty charge indicator or other potential issues with the battery. Try charging and discharging the battery multiple times to troubleshoot, or seek professional assistance for repair or replacement if the issue persists.

Is there a fuse in a Milwaukee battery charger?

Yes, there is a fuse in the Milwaukee battery charger. If you suspect an issue with the charger, check the fuse first before seeking professional assistance. Replacing a blown fuse may solve any charging issues.

Can Milwaukee batteries be repaired?

In some cases, Milwaukee batteries can be repaired. However, it’s best to consult a professional technician for guidance and advice on the best course of action for your specific battery issue. In many cases, it may be more practical to replace the battery instead.

How do I know if my Milwaukee battery is bad?

Signs that indicate a bad Milwaukee battery include reduced run time, difficulties charging or holding a charge, and physical damage such as bulging or leaking. If you notice any of these issues, it’s best to seek professional assistance for further evaluation and potential repair or replacement.

What to do with Milwaukee batteries that don’t work?

If a Milwaukee battery does not work or cannot hold a charge, it’s important to properly dispose of it according to the manufacturer’s guidelines. Attempting to use or fix a faulty battery can be dangerous and should be avoided. Contact your local recycling center for proper disposal methods or seek assistance from your nearest Milwaukee service center.

Do Milwaukee batteries go bad?

Like all batteries, Milwaukee batteries have a limited lifespan and will eventually go bad. Taking proper care of your battery and following manufacturer’s guidelines for charging, storage, and disposal can help prolong its lifespan. If you notice any issues with your battery, it may be time to replace it with a new one.

How do you fix a lithium-ion battery that won’t charge?

If a lithium-ion battery, such as the Milwaukee M12, won’t charge, it may be due to a faulty charger or battery. Troubleshoot by trying a different charger or charging the battery on a different device. If the issue persists, seek professional assistance for repair or replacement of the battery.

How do you reset a lithium battery?

To reset a lithium battery, you can try fully charging it and then completely discharging it three times in a row. This may help recalibrate the battery and potentially resolve any charging issues. If the problem persists, seek professional assistance for further troubleshooting or potential repair or replacement.

Useful Video: Can You Jump A Tool Battery to Revive It? | Milwaukee M12 Battery Jump


In conclusion, the Milwaukee M12 battery offers many advantages for both professionals and DIY enthusiasts. However, it’s important to also consider the potential drawbacks and practice proper safety precautions when handling any type of battery. Remember to always follow manufacturer’s guidelines and seek professional assistance if you encounter any issues with your Milwaukee M12 battery. By taking proper care of your battery, you can ensure optimal performance and longevity for all your power tool needs. So, always stay informed and make the best decision before investing in a Milwaukee M12 battery to enhance your overall experience with power tools. Thank you for reading! Keep building, creating, and innovating with Milwaukee. Happy working! See you soon!