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Charge Milwaukee m18 Battery Without Charger [Avoid THIS]

A cordless toll is of no use with a juiceless battery. Therefore, every manufacturer often provides a dedicated charger for the batteries inside the package.

In a worst-case scenario, the dedicated charger can die for various reasons. This blog post will discuss; How to charge the Milwaukee m18 battery without a charger.

Charge Milwaukee m18 Battery Without Charger

Sometimes, the Milwaukee m18 charger won’t pick up your battery. There is a different solution which I have discussed at the end.

How to Charge Milwaukee m18 (18v) Battery Without a Charger?

The best way to charge an 18V Milwaukee m18 battery is by using an old 18/20V laptop charger or a variable DC voltage adapter that can provide an 18V DC output.

Using a universal drill battery charger is another cheap and VERY-SAFE method of charging a Milwaukee m18 Drill Battery.

The science behind charging a Milwaukee m18 Lithium-Ion battery is the same as charging any battery without a charger.

Milwaukee m18 Battery Terminals [Explained]

An 18V lithium-ion Milwaukee m18 battery has five terminals, as shown in the image below.

Milwaukee m18 Battery Terminals Pinout Identification

First Terminal (+):

The first terminal from the left is the +VE (Positive) terminal. When charging this battery, make sure to connect your source’s positive terminal with this terminal.

Second Terminal (J1):

The second terminal from the left is J1. This terminal is used for communication with the Milwaukee tool and charger for low voltage cutoff and chargings.

Third Terminal:

The third terminal is either a thermister connection that communicates the battery’s temperature or starts a charging signal.

My most probable guess is the second one which is a charging signal. The charging signal turns on a MOSFET to start charging.

Fourth Terminal (J2):

The fourth terminal is also a communication terminal.

Fifth Terminal (-VE):

The last terminal from the left is the -VE (Negative) terminal. When charging this battery, make sure to connect your source’s negative terminal with this terminal.

How to charge an 18V Milwaukee m18 Battery? [BASICS]

The basic science of charging a Milwaukee m18 battery is to provide the 18-20V DC voltage at both terminals by connecting the voltage source’s positive terminal with the Milwaukee m18 battery’s positive terminal and the voltage source’s negative terminal, the negative terminal of the Milwaukee m18 battery.

Note: The Actual Voltage of an 18V Milwaukee m18 Battery is 18.5 Volts. The battery terminals will show 21V when fully charged battery. That’s why it is recommended to charge it at 20Vs.

Below is a schematic of an 18V Lithium-ion Milwaukee m18 battery charging.

The voltage source in the first setup on the left is 0V, so the Milwaukee m18 battery is not charging yet.

However, once the voltage source is switched to 18.0V, it charges. I have applied 20V because the battery we are charging is also rated at 20V.

Circuit Diagram of charging a 20V Lithium Ion Milwaukee m18 Battery.

Once the voltage goes up to 18 V, it starts charging. In reality, it is not that simple. The charging starts as soon as the potential difference rises.

This means that if a Milwaukee m18‘s 18V battery got discharged and went down to 10V, it will start charging as soon as you connect a voltage source above 10. The charging rate is also directly proportional to the voltage difference.

Quick Tip: Get this inexpensive voltage meter by Amazon Basics to properly check your battery voltages while you charge and discharge it. (An expensive one by FLUKE for some serious SCIENCE)

If your Milwaukee m18 battery has discharged to 10V and you have connected it with an 18V voltage source, it will start to charge quickly, and as it approaches 18V, the charging speed will drop significantly.

This same technique is also used in Fast Charging. A higher voltage is applied than the rated voltage of the rechargeable battery at the beginning of the charge cycle. Then, it is carefully reduced to the battery’s rated voltage when it approaches full charge.

The advertised battery voltage of Milwaukee m18 batteries is 18Vs. But a fully charged Lithium-Ion battery must be charged to 20.5Volts before the battery indicator will show a 100% level.

So, charge your battery at 20 volts if you want a full charge.

These variable voltage sources are expensive, but you can get this option from Amazon at a reasonable price. This is another very cheap alternative, but the quality is not outstanding.

Hacks to charge an 18v Milwaukee m18 Battery without a charger

Now, let’s move on to the most exciting part: how to charge a Milwaukee m18 battery without the official charger at home when you don’t have a variable voltage source or official charger.

Before you move on to the hacks, I recommend using the dedicated Milwaukee charger, which is not super expensive (~$31 at the time of publishing) and will save you a lot of effort and RISK.

Ready to Use
Milwaukee 48-59-1812 M12 or M18 18V and 12V Multi Voltage Lithium Ion Battery Charger w/ Onboard Fuel Gauge
  • DUAL CHARGING m18 + m12

So, let’s come to the point. As discussed earlier, you only need a 20V voltage source to charge a 20v Milwaukee m18 battery.

Following are a few ways you can get that desired voltage:

  • Laptop Charger – 18-19V Voltage Source
  • Simple AA Cells – Any amount of voltage can be built up
  • Cheap Voltage Regulators/Converters
  • Another 20V Drill Battery
  • Solar panel

Charge a Milwaukee m18 Battery with a Laptop Charger

Most laptop chargers are rated for 18-20V, which is very suitable for charging an 18V battery.

The process is simple.

Get hold of an old laptop charger. Confirm the voltage output by reading the printed label on it.

Charging a Craftsman 20V Battery with a Laptop Charger

Once you have confirmed that the output voltage is above 18, you have two options.

Option One:

Cut the charging connector and connect the two wires with the Milwaukee m18 battery. Cheap and easy method. You can resolder the wires after completing the job.

Charging a Milwaukee m18 Battery without Charger

Color Codes of +VE and Negative:

Terminal Connections for common Laptop Chargers

Option Two:

This is a little sophisticated method. Try to find a female connector for the charger you already have.

If it’s a universal charger, these connectors will work. Else you will have to cut down the wire and connect these connectors as mentioned above.

For a permanent solution, solder the female connector with the internal battery connections (Positive with positive and negative with negative).

Make a cut-hole for the female connector to sit in; voila, you can charge your battery without the official charger.

Using An Apple MagSafe Charger

An Apple Macbook chargers (The old Megsafe ones) are rated at 14/16/18/20V. You can quickly charge your 20v Milwaukee m18 battery with the 18-20 volt chargers. Do check the output voltage ratings on the back of the charger.

Again, the process is simple: connect the laptop charger’s positive terminal with the Milwaukee m18 battery you are charging and the negative terminal of the laptop charger with the negative terminal of the Milwaukee m18 battery you are charging.

For Apple MagSafe chargers, you will have to go for Option One, where you will have to cut down the Magsafe connector.

Note that the center’s wire will be the positive terminal, and the outer mesh will be negative. Caution: This will irreversibly damage your MagSafe charger.

Charging Milwaukee m18 Battery With Off-the-shelf 1.5V AA Cells

This is an expensive and inefficient way, but it can be life-saving. In an extreme case, when you can’t find any voltage source, you can get hold of simple off-the-shelf 1.5V AA Cells and connect them in series to make up the desired voltage (A voltage equivalent to the battery you are going to charge).

Connect 13 cells in series for a total of 19.5V to charge the 18V battery. They may not fully charge your battery as these cells have a minimal capacity. The charging speeds will be dead slow as well.

You can also get hold of rechargeable AA cells, and they mostly come with a charger, but that will be an expensive route. Still, worth sharing.

Charging a Milwaukee m18 battery with a Cheap Voltage Adapter

The process is the same as in laptop chargers, but cheap voltage regulators are available at electronic shops and online.

Get an 18V adapters from Amazon, which will work great. I found this one to be pretty convincing. It is cheap (Under $15) and has many connectors to connect with the Milwaukee m18 battery.

Ready to Use
Universal Power Adapter 3V ~ 24V 1A 24W
  • Input: AC 100~240V, 50/60Hz ; Output: DC 3~24V Adjustable, Max 1A 24W 
  • It comes with an original 5.5x2.5mm tip and 14pcs frequently used tips
  • The 24W all-in-one multipurpose AC/DC adapter
  • Built-in multiple safety protection systems.

This version comes with many connectors you can use with your Milwaukee m18battery for a long-run solution.

You may find these already lying around at your home, which may have come with electronic devices like Bluetooth speakers, min fans, or toys. Do a thorough search.

Jump Charging Milwaukee m18 battery with another 18V battery

Jump charging a Milwaukee m18 battery with any fully charged 18V battery is also a great hack.

For example, if you have another drill battery with a working charger, you can use that drill battery to charge your battery.

Again, science is the same. Ensure the other battery is of the same 18v voltage and fully charged.

Now connect the terminals in the same polarity. Positive with positive and negative with negative.

An image of a Milwaukee m18 battery charging another 18v battery

As shown in the image above, you will have to use jump wires for the connections. It will not be a solid solution but can work in an emergency.

Check this video for a demo.

Charging a Milwaukee m18 20V Battery With a 20V Solar Panel

Solar Panels are a great source of DC Voltage Source. However, there is one problem. The Output voltage is not constant and varies due to the change in sun direction and temperature.

You can buy pre-built panels with voltage regulators etc. However, they are expensive.

Ready to Use
Foldable Solar Charger with DC(20V/1.8A)
  • Compatible with Most Devices
  • Design with Kickstands and Auto-restart
  • IP54 Waterproof & Durable Design
  • Portable and Highly Efficient Monocrystalline Panels
  • Best Quality and Service Support

Here is a sound 20V solar system that can charge a Milwaukee m18 battery without a charger.

If you already have a solar panel, make sure the panel has an output of 20Vs.

Do Milwaukee m18 batteries have a built-in Undervoltage cutoff?

Milwaukee m18 batteries communicate with the tool directly but don’t have a cut off at the main two terminals.

The cutoff voltage is built-in inside the Milwaukee Tools and Charger. The tool will stop working as soon as the voltage drops to a certain level (15 V, to be precise).

Similarly, the charger will stop charging once the voltage hits 20.5 Volts.

Sometimes, a fuse inside your battery can go off. In that case, you need to either open it and replace or take it to an authorized repair shop.

Why My Milwaukee m18 Charger is Not Charging My New Battery?

The Milwaukee m18 charger needs a minimum of 3-5 volts at its terminals to detect your Milwaukee m18 battery.

If it has discharged completely, the charger will not be able to detect it.

To fix this problem, charge your battery with something else, as discussed in this blog post, and plug it back into the charger.

You can do so by applying a 12V battery connection on both terminals to charge it for 30 seconds.

Make sure to connect the positive terminal of the voltage source with the positive terminal of the battery you are charging and the negative terminal of the voltage source with the negative terminal of the battery.

Additional Read:

  1. 09 Best Cordless Drills for home use
  2. How to Fix Battery Discharge Warning in Your Car?
  3. How to drill plexiglass without cracking?