Up until last week I was reliably getting 2.5 to 3 days of battery life with my 4S. I really don't use it that much. 99% of the time the phone is in standby mode. I am on 5.0.0.
Last week, suddenly, my phone started chowing battery. This literally happened overnight. I couldn't even keep the battery going for more than 8 hours without a charge. Aside from a couple phone calls and a 20 minute game of Angry Birds the night before, I didn't use the device the whole day. It is worth mentioning, Angry Birds mysteriously crashed on me twice that evening. Something I'd never seen before. Also worthy of mention, I'd been getting in to the habit of "cleaning" out my apps at the end of the day.
I tried *EVERYTHING* (short of a full reset) to get the battery life back. I disabled EVERYTHING. Not even airplane mode helped.
In a last ditch effort I fully powered the phone off and put it on the charger for a night. During the night the phone automatically powered itself on and I subsequently powered it back down and continued to charge it. The next day, the battery life was slightly better...I managed to get about 16 hours but, not nearly as good as before. I noodled with more settings and played some more Angry Birds. I did not "clean" my apps at the end of the day like I had been. Last night, I charged the phone again while it was awake and today it is back to normal. The phone has now been running for almost 10 hours and has only consumed 10% of its battery life.
My suspicion is that this is a result of a software issue it is an unhandled thread or something of the such. It may be related to a specific app. Angry Birds?