why is My note4 is shutting off

[Epicbk]

When my note4 gets to 21% it cuts off like it's completely dead. Then when I turn it back on it shows it's at 0%.. what could be the reason for that it wasn't doing that before....

 

[Epicbk]

Thank you

 

[muzzy996]

It's most likely due to a failing battery (may have a blown cell inside it). To test, take it out of the phone lay it on a flat surface and alternate pressing on each side (flip it over and repeat). If the battery wobbles means it has a bulge from a blown cell.

Is swelling always indicative of a blown cell, and a blown cell always results in swelling?

 

[IAmSixNine]

LioN batteries are sealed units. Typically when they go bad a chemical reaction happens and they off gas which causes the battery to swell. So yes swelling is typical of a battery being bad or going bad.
I have seen a few other threads where people report their phones powering down around 10 or 20 percent and usually a replacement battery fixes the issue. Its a good place to start.