How can I tell why my sleeping phone occasionally gets warm (and battery is draining abnormally)?

Question

My two Android phones are doing the same thing, Motorola Milestone and Samsung GS3. From time to time, it is sleeping in my pocket and it will start to get warm and the battery is then draining quite rapidly. I guess it must be caused by an application that is stuck running in the background so I am checking:

• Task manager, but none of the applications seem to be using more CPU than any other, they are mostly all close to 0%.
• In "Battery Statistics" only "Phone Idle" shows quite high battery usage so it does not tell me if there is a problematic application.

Currently I just reboot the phone to solve the problem but I would prefer if I was able to find the problematic application so I can close it.

Answer 1

I think this could maybe be because of several things:

• You have a bad network connection. If you are on a location where there is a bad network connection, your phone will have to try very hard to keep this connection enabled. Or maybe that is also possible when you are walking in locations that have a bad connection to the outside world (in the basements of some buildings for example).
• Sometimes if you are using Live backgrounds, that drains the battery too.
• Another possibiliy is that your phone is syncing in the background. If you have for example enabled that calendars have to stay synced (and you have an enabled data connection), then your phone will on regular bases connect to the internet for some updates. I don't think (but I'm not sure though) that this would show up in your task manager.
• It could also be that something like your GPS or Bluetooth is enabled, and becomes a problem (although I think this would show up in your task manager)

I would suggest you have a look at the services that are enabled, even when your phone is in standby mode (Bluetooth, GPS, syncing..)

Answer 2

I know this may look like common sense, but maybe you could simply take a piece a paper and note every single launched application whenever this happens.

After 5 iterations, you should have a pretty accurate idea of the culprit.

If not, as Tim mentionned, you should take a look at the logs to have a better understanding of what's going on on the system itself.

PS: Using a paper RATHER than an app would be encouraged, because the notepad app you would be using COULD be the culprit itself :)

Answer 3

Check your phones settings > Wifi settings, to see if wifi is selected to "Always" stay on. If not you can change it to go off whenever the screen goes off.

This may help with some of the battery drainage .

Update:

@jmbouffard. - While you are in settings > About Phone > Battery Use, have you clicked the graph at the top? Sometimes only "phone idle" will show but clicking the graph will give you better details.