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Well it is still in beta, and beta versions of iOS do not have a great track record for battery life simply because they do not contain all of the optimizations that a final version has. It is an incomplete operating system, and that is why it is in beta.

In other words, it doesn't really matter what the battery life of the beta is because the final version will be (hopefully) better
 
It's definitely worse than it was with iOS 10, but since I use a Smart Battery Case my iPhone still easily lasts a full day, instead of the usual two. But like jsook724 says, it's a beta, a non-complete iOS update. And not to mention that with big updates, people (including myself) tend to try out every feature causing battery life to drop more significantly. I already see a difference today compared to yesterday for example, since I've been using it more like I did before I installed iOS 11 beta 1. Like, more realistically you know? And of course Spotlight does a lot of indexing after updating, that'll account for a slight difference as well.
 
Or how about the battery life on iPhone 6 with iOS 11? I know there must be a number of people like me willing to upgrade and put up with a few milliseconds of delay on apps, so long as they iPhone 6 battery doesn't get any worse....
 
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