I just joined this forum for this problem, and thought I would chime in. I used to get several days out of my Samsung Galaxy S5 battery because it's basically just turned on to receive calls and texts, but I rarely use it for anything else so screen time is less than 4%. I have had the phone for less than 4 months. Less than a week ago, the phone beeped because it was going dead, which was odd because normally it would have had over 50% charge remaining. Now, I cannot even go 20 hours with it just sitting on the counter unused, and it is warm to the touch. This is what is found under "Battery":
Cell standby: 16%
Android System: 16%
Android OS: 12%
Google Services: 11%
Device Idle: 10%
Wifi: 10%
Voice calls: 7%
Lookout: 5%
Screen: 4%
Something has clearly changed with this phone, and I don't know what. I have tried restarting the phone, turning it off for a while, then re-booting, all to no avail. I am using almost 10% an hour at times without even using the phone. It is a joke.