Samsung Galaxy s5 shuts down by itself and the battery becomes 0%

[Android Central Question]

I was using Twitter and just scrolling through my feed for like about 5-10 minutes, my phone battery was around 80% then my phone just randomly turns off and when I plug the charger to it the phone turns back on and says 0%. This happened to me while I was watching youtube, my phone was at 60-70% and it turns off. Sometimes it turns off and just loses 10-20% power too. Why does my phone keep turning off by itself and loses power?

 

[Kodak2]

It does sound like the battery has come to the end of it's life. This is not unusual as the S5 phone is now about 4 years old.