This would be my advice. These meters are really very fickle things and they can get pretty far out of whack, resulting in lying about the charge levels in both directions - has more than it says & has less than it says. The first one can result in it seemingly going from 30% remaining to completely dead in a matter of minutes. The second one can result in it appearing to be low, yet continue powering the phone for extended periods of time (in one example 8 hours playing music while showing 5% remaining the entire time).
It's not unusual for the phone to consume more power for a while after such a sweeping update (and even after minor service updates), since there may be large caches of memory that were wiped clean in the process, various subroutines that were stored for later use that now have to be re-poplulated. Then there's various updates to software, email and account syncs, etc., so all told the phone typically consumes heavily for the first couple days.
Yes I am def aware of that and had no problem with the battery draining fast after the update. The problem came when I tried to charge the battery after it was dead.
ALWAYS use the wall charger to be sure you are getting a full charge. Only use USB if you need to get a quick 10% to 20% boost.