many issues on HTC One M8

[Android Central Question]

I have a HTC One M8 since Fall 2015 and lately it has become unbearable. Among the various issues I'm experiencing:
- phone shuts down suddenly even with battery even up to 48% (!!!!) when running "too many apps" - example, I have Gmail, Facebook, Messenger running in background with nothing going on and when I start a phone call on WhatsApp or watch some video on YouTube, the phone goes blank as if it had 0% battery left (needless to say, this is the most annoying issue)
- sudden change of settings, eg shuffling and change of icons in drop-down control panel
- several applications repeatedly and suddenly forgetting log-in settings and asking me to re-activate them
- new entry: at the third year of life, I start to get occasionally the tips from the OS on how to use various features, eg the camera....
Has any other possessor of this phone experienced this? Would rooting help or should I just purchase a new phone? I could go for the latter, but it feels wrong that suddenly it stops working properly. True that it's not as fast as it used to be, but these behaviours, appearing all together, sound weird

 

[B. Diddy]

Welcome to Android Central! The battery is likely failing -- sudden shutoffs at higher battery levels is a typical sign. Since the battery is not user-removable, you'd have to bring it to a repair shop, or consider getting a new phone. These days, a 3 year-old phone is pretty old, especially if you use it pretty heavily.

In the meantime, try wiping the cache partition, which can sometimes help with general issues: https://support.t-mobile.com/docs/DOC-10672