Been just three days but with my typical daily usage my 4s almost always still had a 50% charge by 5pm. Since I went with 5.1 on Tuesday I'm left with 1/4 charge by 5pm. Battery performance before 5.1 for me was just fine, I never had a complaint but on Weds I used it heavier than normal and it went down to 1/4 by 1pm. Thrusday and today (Friday) typical usage, and even turned off location services didn't seem to help. On the bright side, Siri is more accurate and noticeably faster. The phone is more stable and apps aren't crashing as much. I'm probably just one of the lucky few with a dyslexic phone.