Since there are a lot of SGS2 users complaining about batterylife, overheating while charging and draining like a sewage pipe, I thought I share my solution. I've had the problem myself, the first thing to try is a clean install. Or at least wipe cache and dalvik. Wiping battery stats might also help. Then, make sure you don't use the stock Miui lockscreen. Don't use it. Try any other from Miui themes. Let the battery drain until it's ready to die. Charge it back up, let it sit on the charger even after it's full. Chances are you won't be bugged again. I can't guarantee it though, since I'm using another kernel (siyah 5.0.1) as well.