Thank you! You're describing exactly what I'm experiencing. I feel like I'm going crazy because everyone is giving me tips like disable location services, disable background app refresh. THAT'S NOT IT! Yes these tips and tricks all give you a little bit better battery usage. But this is not nearly the level of drainage we're talking about here. I had my phone on Low Power mode AND airplane mode turned on. It was nothing but a dumb brick until I turned it on so I could see if my SO sent me a message or not. The phone would drain roughly 10% every 30-45 minutes. After 5 hours of being in airplane mode and low power mode, and disabling airplane mode once every 45 for about 1 minute to see if I had a text, my phone went from 100% to 0%. Btw this is a three week old iPhone 6S. With my old iPhone 6 on IOS 9.1 or 9.2 I don't remember, I could put my phone in airplane mode at night and during a 6 hour night it would drop maybe 2-3%. Where is this MASSIVE difference coming from? You can't tell me it has to do with these little tweaks like turning off location services. I'm not saying those don't help, I'm sure they can extend your battery life and maybe even double it. But still, we're talking about a different level of draining here. This is from 100% to 0% during a 5 hour period on airplane mode. It shouldn't be like that. That's a factor 50 faster than before. And the stupid Battery app does NOT help at all, it just shows you which apps use the percentage of battery. But it's not showing where this massive drainage is coming from. Yes if tried rebooting the phone, yes I've tried backing it up and restoring. I've even downloaded the IPSW file and forced an installation using iTunes, set it up as a new phone and installed all my apps and recovered all my photo's. That's the last thing I've done, and it's still draining like crazy. People told me I had to wait 24 hours to let the phone settle in, I just did. In the last 30 minutes of standby it drained 6%. I didn't touch it, but this time it wasn't in airplane mode. It'd say it's marginally better, but still way too high. This means in 8 hours of not touching my phone it would go from 100% to 0%. That's still bad, very bad. I'm at my wits end here. And I don't want another phone, otherwise I would have brought it back and gotten an S7 or something. But I love my iPhone, I just want the thing to work.
What it seems like to me, is a particular app or a hidden IOS process that's causing it. Reason I say this is because I restored my iPhone 6 backup when I first got my 6S and the battery problem didn't exist. It wasn't until after a week or two of using it that it got this bad. But I can't seem to figure out which one. I've removed some apps already, but nothing seems to make this massive change.
Since this is a brand new phone I'm thinking of just going back to Apple with it, I just don't want to go through all the same steps again only to get back to where I am now. Any other advice anyone?