How to tell what is killing battery intermittently

[AC Question]

My HTC One M8 (Sprint) has worked fine, battery lasts all day mostly. But recently, about 1/2 of the time, the unit gets hot and the battery is just sucked dry! Like right now, after being off charger for 5 hours, I'm down to 42%. It doesn't happen all the time, but frequently. Sounds like maybe an app is running away with itself. How do I tell what's draining it? I looked in Settings-Power-Battery usage, and nothing looks too far out (mail at 21%, Google Play services 14%, FB at 11%, everything else less than 10%. So how do I find what's causing the battery to get hot and drain so quickly?

 

[B. Diddy]

Welcome to Android Central! Charge up to 100%, then let it drain to 20-30% with normal usage, without charging in between. Then show us:

1. The main Settings>Battery screen.
2. The fullscreen battery graph screen (which shows Awake time and Cell Signal Strength).
3. The Screen category (to see total Screen On time).
4. The Cell Standby category, if present (to see Time Without Signal).

http://forums.androidcentral.com/am...ide-how-post-screenshots-android-central.html

Poor cell signal is a common culprit--when the phone is heating up and draining battery, see what the cell signal strength is like.