Do your BeatsX headphones no longer work? It's most often a bad battery and it's pretty easy to repair yourself! Here are some common symptoms to help you diagnose:

Your headphones only turn on when plugged into the charger
Your headphones flash red and white
Your headphones have a "pink" (red and white) LED
Your headphones only play for a few seconds before disconnecting

Supplies

Before you begin you should check if you have all of the following:

Replacement battery (AliExpress)
Helping hand or a clip to hold your headphones steady (Amazon)
Soldering iron with a fine tip and solder (Amazon)
Optional: Solder flux (Amazon)

You can also buy a pair of used or broken headphones on eBay and salvage an original battery, but you're taking a risk because it could be dead!

Step 1: Opening Your Headphones

Open your headphones

Near the right ear piece of your BeatsX headphones there is a control with a power button. This will be the area we focus the repair on. Begin by slowly and firmly flexing the rubber joint closest to the power button. This motion will begin to wiggle the joint free from the shell.
The shell contains the battery and control circuitry so we want to be careful. Once the joint is beginning to wiggle free from the shell very gently begin pulling apart. The goal is to separate the shell from the joint about 3mm or 1/8". Once there's a suitable gap proceed to gently push the rubber grommet on opposite end of the shell into the shell. You may need to gently wiggle it back and forth while slowly pushing in.
Once the grommet on the end opposite of the power button has been loosened go ahead and slide the entire assembly out of the shell. You may now mount this in your helping hands or clip as demonstrated in the attached photo.

Step 2: Soldering

Desoldering Your Battery

With the shell mounted in your helping hands you may now proceed with soldering your headphones. However, before you apply heat to your headphones let's test that the soldering iron is up to heat.

With your soldering iron plugged in and turned on for 60 to 120 seconds apply a small amount of solder to the tip of your soldering iron. Does it melt almost immediately? If so then you are ready to proceed. If not, wait 10-30 seconds and repeat the exercise before continuing.
Using the tip of the pre-heated soldering iron, apply 3-5 seconds of heat to the gray, black, and red wire terminals individually. As you heat the terminals it's suitable to apply a small amount of pressure to lift the battery from the terminals but do not pull hard. Pulling hard on the wires could lift the embedded metal pads from the electronics PCB, which may be irreparable for all but skilled electronics repair people.

Step 3: Soldering & Closing Up

This step will cover the process of soldering the new battery and closing up. Depending on the battery you have purchased, you may find the new wires from your battery are long and wiggly. Take your time and use a pair of tweezers to hold the wires while soldering if necessary.

Line the wires from your battery up based on their original alignment, also indicated in the attached photo. Line up the wires on their respective terminals and simply apply a small amount of fresh solder with the tip of your soldering iron to the wires. If you apply too much solder you can often pull excess off your terminal by touching the tip of the iron to the excess blob.
Once the wires are reattached you're ready to close up. If this is the first time opening your BeatsX there may be remnants of clear sticky tape around the rubber joint which you removed from the side of the shell closest to the power button, remove any remnants of tape before proceeding.
Slide the assembly into the shell while maintaining gentle pressure on the grommet in order to guide it through the end of the shell. When the grommet is mostly through the end of the shell and there is a 3mm or 1/8" gap on the joint closest to the power button you can proceed to apply firm pressure to the joint closest to the power button. The goal is to re-insert it into the shell. When the joint closest to the power button is successfully reinserted you can pull on the grommet in order to seal the remaining gap.