Maybe it's (all) hardware related.... just a reset of my network (carrier) settings just bumped my battery from 76% to 70%.
And possibly in some cases I am lucky to have a full battery and on another day some sort hardware related bug/setting or background app just wipes away all battery power....
My iPhone 4S is a little more than 2 years old at the moment with daily/nightly battery charges (so around 800 charges in total).
Or am just guessing here?
I'm just coming into this conversation so I'm sorry if this ground has already been covered.
I've had issues with battery life in the past with my iPhone 4 that was really bizarre cell data usage even when I was connected to WiFi. You can read about the problem I was experiencing in this rather long thread here: http://www.neowin.ne...er-than-normal/
It may give you some ideas on troubleshooting your battery life as well.
The main thing I'm wondering is this: Is your phone unusually warm? If the device is hotter than normal than it is likely using more energy than normal. That could be due to a number of things, but it may not be that the battery has gone bad. There could be something else that is sinking the energy and heat dissipating from the device might be evidence to that.
If I were you I would run a reset on the device, clear everything off of it, don't add even your email connections to it. It may not be a very useful device, but it will allow you to at the very least observe if the problem exists with the iPhone in its "most default state" or if it is brought on by a server you are connecting to or an app that you have downloaded. I recall having issues at one point with my work's exchange server where I think it was adversely effecting my battery life.