Closing apps can actually hurt battery life (iOS is very smart about suspending apps and closing when they need to be). Go into settings>general>usage>battery usage and see what's killing it. Most likely you'll need to reset your network settings and/or all settings.
My 5s has been getting around 6h 45m of usage time on iOS 8 and 8.0.1 and 8.0.2 consistently. It's down slightly from 7.1.2 but its only maybe an extra 30m on usage.
Haven't noticed this at all. In fact, the battery drain on standby has really gone down. I suspect that it's because I use wi-fi calling and my phone doesn't need to lock onto the weak voice signal in my neighborhood. But, I haven't confirmed this yet.