So I use to have pretty decent battery life after only 3 weeks with the phone. On my longer (12 hours on the road) days, my phone would get home with still ~30% battery. Recently, I have been getting huge battery drains. First 3 hours of the day, I played music (offline music) on my 30 min drive and then phone was in my pocket during class. Got to my car and had 70% battery. Got to work and charged it for about an hour and downloaded an apk for betterbatterystats. Downloaded it, unplugged my phone, set it aside, and waited. Here are the results:
.....
Well apparently I can't post pictures yet. Battery started at 84% and is now at 44% in 2h 28m. From the betterbattery app, "bam_dmux_wakelock" has used 10% of my battery in 12m 51s. The android native battery app says the "Android System" is at 59% of the battery used. And the device has been idle for almost all of that time (screen idle is at 2h and 10m). So clearly something is running in the background reaping havoc on my battery.
Any ideas?
It looks like you may be having the same issue I was (still am sometimes). See here: http://androidforums.com/samsung-galaxy-s3/628086-yet-another-batter-help-request.html


