Thanks to some of my developer friends on Twitter, I learned that the majority drain has Siri to blame!
Due to Siri being contextual and and having features such as the new smart GPS locations, Siri dominates battery. Turning off Siri GREATLY IMPROVES battery. While it helps save a lot of battery, I found that even with Siri off, and 'low power' mode on, my battery is still MUCH worse than iOS 8.
With iOS 8.4 I usually get, nearly, 24 hours of standby, and 12 hours of active usage on my iPhone 6.
With iOS 9 Beta 1 I get 5 hours of standby and 2 hours of usage on my iPhone 6.
(With iOS 9) I charge my iPhone 6 up to 100% battery, and unplug it around 11 pm. I go to sleep without using my phone and when i wake up at 6:20 am (7 hours later) my phone is at 32%. Not sure why I get better usage time than standby time sometimes, but, just telling you what I know!
All my iPhone settings are configured to the lowest settings. Background app refresh has always been off for me. I recommend that EVERYONE turn background app refresh OFF no matter what, as turning it on honestly doesn't make a difference in usage features (it has no real use with it on), but turning it OFF will make a huge difference in battery. I've been doing this since Background App Refresh has been a setting, and I've not been left out of using any features due to turning it off, the only thing I've experienced is BETTER battery.
Also, there are quite a few location services settings turned on that drain battery, and aren't useful to the user. If you navigate to Settings > Privacy > Location Services and scroll to the bottom and select "System Services"
Turn off everything except 'Find my iPhone". If you use the 'share my location' feature in messages then you can and should keep that settings turned on to allow you to continue you to use the feature.
If you use spotlight for location based searches, keep that on as well. Near the bottom, turn on Routing and Traffic if you use Maps a lot, or jut want to have the feature on in case you ever do need to use Maps. Otherwise every other settings in here is NOT crucial by any means, and should be turned off to conserve battery, whether you are on iOS 7,8, or 9. I've always turned everything off, except for Find my iPhone and Share my Location, and I have never had any problems; only better battery!
Everything else in here drains your battery on system aspects that users don't actually interact with. Things like Call Network Search basically tracks where cell servers are and sends the locations to Apple. Things like this kill your phone battery, and don't truly affect you. You can Google what each one does if you are nervous to turn them off, but trust me, I've had them off for years, and I get great battery (as long as I'm not on iOS 9 Beta software LOL).
If you accept my advice, I can guarantee better battery for everyone! In order to attain better battery, turn Siri OFF and turn Low Power Mode ON (and keep it on until the issue is fixed). System Location Services should always be off, other than the ones you specifically know you use (Find my iPhone, Share my Location, and Routing and Traffic).
