Power being eaten by screen usage This morning, when I woke up my phone was out of battery power. So when I checked the battery usage I see the message Display had been used 90%. 

This kind of situation had never happened to me before. I was surprised as I always turn off my mobile screen by clicking the power button.


Why has this happened even though I turn off my screen?
How can I avoid that kind of situation from happening?


Android Version: 4.0.3

Mobile: HTC One X
Keep in mind that on the Battery Usage screen even though per-app breakdown always adds up to 100%, it does not represent the full capacity of your battery, but rather only the used portion.  In other words, if your phone is reporting current battery level of 65%, the breakdown is for the other 35%.

Since nothing really happens overnight, it's not unusual for the "Screen" to be shown as taking 90% (again, that's 90% of the used up 35%).  That just means you've used the screen for a little bit, and then nothing else consumed too much battery.

It's possible that you had too little charge left over from the day before and not having the phone plugged in overnight pushed it over the edge.