I have been using CPU SPY to determine the battery drain issue, especially when your phone is on ICS and runs hot. It is a sign of trouble and there seems to be no way around this as it is connected to the apps you have running on your phone.
Many apps are not designed to take advantage of ICS, and if you happen to have a few lines of code that confuses the system, it will start to run in a loop. Often this happens when the app in question fails to execute a command or exit. This is what causes it to run hot. If you check the background apps running on your phone, nothing will show up. Terminating RAM routines and reducing the number of background apps also does nothing to solve the problem since they automatically start up again once you do this.
The temporary fix is to turn off your phone, and in some measures, taking out the battery.
Remember in the old days of Microsoft Windows where you have an extension clash and have to manually weed out the culprit? I guess this is the same method you can employ here. Use this free app called CPU spy to monitor your habits. In a deep sleep state, that is when you are not using the phone, the chart should look like this. If however the phone is running haywire, you probably will see the other CPU states running amok.
Right now, some users on forums have indicated that the stock email app is to blame. Since I have not tested this, I would appreciate if you guys out there can give your own observations after installing CPU Spy.