I have IOS 8.4 and my battery lasts about 8 hours. I keep my brightness either mid way, or less. Mostly less. I only have a couple of apps, mainly snapchat Facebook Instagram and messenger. I keep my Bluetooth off, wifi off when not in use, and data when not in use. I close the apps after using it as well. Is there any way I can increase my battery life to more than 10 hours, preferably 15hours?