Macbook always freezes when under 20% battery, turns off and turns on exactly like the image I posted and then goes off.

Hello Fsilvalexandre,

We suggest that you use Apple Diagnostics to test your Mac. You can use this tool in order to diagnose if there is an issue with your computer’s internal hardware.

Here's how:

"Prepare your Mac

1. Shut down your Mac.
2. Disconnect all external devices except keyboard, mouse, display, Ethernet connection (if applicable), and connection to AC power.
3. Make sure that your Mac is on a hard, flat, stable surface with good ventilation.

Start Apple Diagnostics

Determine whether you're using a Mac with Apple silicon, then follow the appropriate steps:

Apple silicon

1. Turn on your Mac and continue to press and hold the power button as your Mac starts up.
2. Release when you see the startup options window, which includes a gear icon labeled Options.
3. Press Command (⌘)-D on your keyboard.

Intel processor

1. Turn on your Mac, then immediately press and hold the D key on your keyboard as your Mac starts up. 
2. Release when you see a progress bar or you're asked to choose a language.

View the test results

Apple Diagnostics shows a progress bar while it's checking your Mac:

When testing is complete, Apple Diagnostics shows the results, including one or more reference codes. Learn about Apple Diagnostics reference codes.

To repeat the test, click “Run the test again” or press Command-R.

To restart your Mac, click Restart or press R.

To shut down, click Shut Down or press S. 

To get information about your service and support options, make sure that your Mac is connected to the internet, then click ”Get started” or press Command-G. Your Mac will restart to a webpage with more information. When you're done, choose Restart or Shut Down from the Apple menu.

Learn more

On an Intel-based Mac, if you can't start Apple Diagnostics with the D key, try these solutions:

• Press and hold Option-D at startup to use Apple Diagnostics over the internet.
• Make sure that your Mac isn't using a firmware password."

If the test results include a reference code and you need more assistance, we suggest that you reach out to Apple directly. You can follow this link to connect with them: Get Support

Take care!