Using the wall charger will fast charge your iphone to 80% then trickle charge to 100%, This is the best way to charge your phone. Connecting to the USB uses a lower power and takes longer to fully charge your iphone, so it will take longer to fully top off the battery even though the indicator may say 100%.
As for battery usage, when i 1st picked up my phone the 1st couple of days it drained the battery fast. I had to charge it before the day was done, for this reason i went and bought the Mophie juicepack plus for my iphone. How ever after the initial few days it seems my phone is getting better with battery power. When 1st activated the WIFI was turned on, I rarely use WIFI so i turned it off and only turn it on when i want to use it. The Blue tooth was also on. I don't use blue tooth for anything so i turned that feature off. My mail was set up to push and i changed it to fetch every hour. Doing these changes it uses only about 50% of battery per day. Thats with moderate use, getting email, talking on the phone, text messages, some internet surfing, and i have sevral apps i check several times a day. I may take back the mophie juice pack plus cause if my phone stays like this i have no need for the extra battery pack.