Why does my battery on my iPhone 6 run down by itself?

I updated my iPhone to the iOS 10 update and ever since then the battery hasn't been good and it runs down when I'm not even using my phone. I don't understand why because I turned things off in settings to try to help the battery. I turned off all notifications and I turned on auto brightness and I also turned off the spotlight search bur that didn't help the battery at all. I've also tried charging my phone and then turning my phone off and turning on airplane mode and then I would turn my phone off again and turn off airplane mode but that didn't help either. I've had this iPhone for a little over 2 years though.

Are deleted photos from an iphone gone for good?

When I was sleeping, my friends took a bunch of ugly & embarrassing pictures of me. Over 5 of them! I deleted them out and out of the recently deleted file, but I'm paranoid that you can still recover them. They are not backed up to anything because of how recent, and the last time I backed up my phone was when I got it 3 years ago. Nothing is synced on my phone. Are they gone for good?

How much does the iPhone 7 cost?

I'm a minor and I so far I have $569 saved from my job. ( I'm 16 and I have a job ).

But I just want the iPhone with the charger and headphones.

How much will it cost and I don't want a contact I just want the iPhone.

How does straight talk work?

Can somebody please explain how straight talk works. I have an iPhone 6 through Verizon. Could I switch over with my iPhone? And if so how does the data plans go how much do you get they say unlimited but I find that hard to believe for only $45