Why is Photos using my battery for Audio like this? My new iPhone 7 (which I set up as a new phone and not from a backup) is reporting strange battery usage due to Photos. 

It's saying that 15% of the battery has been used in the last 24 hours due to photos being onscreen for 5 minutes, using Audio!

What's happening?
It could be because you have been watching some of your own videos in the photos app. It doesn't mean that the photos app has been doing this for the full five minutes, it just means that there has been audio playing in that app at some time, and the rest of the time could be other things.