Why is my battery on my HTC One M7 dying randomly around 20-50%?

[AC Question]

Its a M7 from T-Mobile and hasn't been rooted or anything and its never been dropped or dropped in water or anything and its also running android lollipop. I got this phone used on eBay and it was sent back to the factory to get the camera issue fixed and it was very good when I got it a few months it started acting up and would die randomly from 20-50% and its frustrating

 

[Jon_Doh]

I've had this phone, AT&T version, since it came out. Once about a year ago it started running hot and the battery began discharging in big chunks. I had not installed any new apps, but I had updated some I tried everything from installing battery monitors, disabling apps and running Greenifiy but nothing helped. Finally, I cleared the system cache (Google how to do it) and a factory reset. The problem was solved and I've enjoyed great battery usage since.