Why is my phone shutting off at 50-60%

[Samsungnote3fan]

OK so before i got this phone (samsung galaxy note 3) this was my moms phone and she had no problems with it. I was in class one day and my teacher wanted me to turn off my phone which i did, after class i turned it on, in which 5 minutes later it shut down on me. That was the first time it happened so i thought nothing of it thinking it was a one time thing. It happens a lot so its annoying. This was back in november or october of 2016. I would like for this to stop happening so i can shut my phone off and turn it back on without it doing it to me again.

 

[SpookDroid]

Sounds like the battery is going bad. Have you tried changing it?