Crazy battery drain in just a few hours
I've been searching various forums for a fortnight now to try and diagnose an SII issue I've been having and Google inevitably brings me here. Unfortunately, the numerous threads on battery drain don't match the problem I've had and the solutions haven't helped.
Around two weeks ago I noticed the battery life on my handset was really terrible, draining in hours. I had been using it quite a bit at the time so assumed this was the cause. However, lately it has been draining within around 6-10 hours even when idle, usually dying completely overnight despite a full charge just before then. I don't have a huge number of apps installed - maybe 20, fairly standard ones like Twitter, Facebook, Amazon, no games and no 'battery defender' style apps. It's not rooted (it's 4.0.3) and I can't root it for other reasons.
The battery drain was a nightmare, basically going from power point to power point just to keep it topped up enough to use and it was draining during idle time and deep sleep. I very rarely ever have 3G, GPS or Bluetooth switched on. Wireless is on most of the time and it generally does have a signal in the two places I spend most time (home and work). It also has a strong Vodafone signal since I'm living in a major city centre.
I tried a few things:
1. Uninstalled all but the most-used apps I had. No change.
2. Uninstalled everything it was possible to uninstall. No change.
3. Installed BetterBatteryStats and CPU Spy. BBS plus many hours of searching kernel/partial wakelocks and so on showed nothing that looked odd at all, certainly nothing taking up a lot of time or regularly stirring the phone. CPU Spy showed it did deep sleep when idle.
4. Factory reset. This included no app installations except BBS, disabling the likes of Social Hub, Gaming Hub and all other stock apps I could. No tethering or wifi sharing, no wifi, no 3G, no GPS, no Bluetooth, nothing running. It was basically a handset sitting there doing nothing. BBS showed nothing odd that I could see but the battery still drains in hours. No partial wakelocks and a tiny number of kernel wakelocks taking up next to no time and occurring a handful of times. No change.
5. I charged it before bed, took the battery out and left it until morning. In the morning it was down at 79%. This seemed weird so I bought a brand new genuine Samsung battery and gave that a try. No change in the 6-10 hour drain but taking the battery out overnight showed no drain now.
6. The weirdest of all. I charged it fully before bed, switched it off over night and it was drained completely by morning. That seems crazy to me. I can fully understand poor software or bugs draining a battery but not when a handset is switched off.
I am lucky enough to be able to get a new handset through work but this issue really annoys me. I took very good care of the phone, never installed anything crazy, didn't over charge it, the handset never got warm at any time, I'm careful with Wifi/GPS/Bluetooth/3G and location services, yet I ended up with an effectively useless "mobile" phone.
Is there anything that comes to mind that could have caused this? Point 5 above made me think it was simply a battery issue and maybe it partly was (with two batteries, how unlucky) but point 6 is just crazy. What could cause a handset to drain a battery under these circumstances?
Thanks for any advice!