Battery life is poor and somewhat strange for me. On a 6s.
I've noticed that over the recent betas and now in the GM, battery life drops like a rock. I'll get 7-8 hours and a couple hours of usage and be around 20-30%. Not good. I use my phone in the exact same manner every morning on the way into work. On 9.3x, I would be around 86-88% when arriving to the office starting from a full charge. On 10 GM, I come in around 78-80%. I charge my phone once I get to the office. What's interesting is when I do charge in the morning with iOS 10, in just 10 minutes of charge from a MBP, the phone goes almost immediately from reading 80% charged to 90% charged.
I was wondering being a year into the phone use, if the battery was going bad. So I took a walk down to the apple store. When I did this last week their diagnostic tools were not working with iOS10 GM. So wanting to know if it was a battery issue or perhaps a iOS 10 issue, I dropped back down to 9.3.5 in the store so they could run the diagnostics. Battery health was shown to be at 96%, so it's not a battery issue. The genius said he's seen a few other instances where people have come in with battery questions and they were running iOS10.
What does this all mean? I don't know, but figured I'd share my observations.