We don’t know what kind of battery will be powering the new iPhone 7, but the new version of iOS is going to come with a Low Power Mode that should help users make the most out of their battery life. There are also rumors about other forms of optimization in iOS 9 as far as battery performance goes.
We can only wait for Apple to release some official information about the new phone at the moment, but the company is as cryptic as usual so we likely won’t hear much until they are ready for the announcement.
Which, from the looks of it, isn’t going to happen for at least another month now. If they really are targeting September for the phone’s release, then we probably won’t hear anything about it until at least August or so, and even then it might be a very limited release of information, closer to a teaser.