Hi - I'm curious about what's the best battery case for iPhone 7? I'm interested in a slim battery case, but one that also is "always on," much like how Apple's own smart battery case is "always on." Or it could be a case that stays "on" until the battery is specifically turned off. (Think Mophie's battery case for the iPhone 6S, for example - it has a switch that you can leave "on" all the time.) Any leads? Suggestions? Thanks!