One tip I happened upon by accident, but I don't think OP mentioned:

Start the Strava app recording the ride, then hit the Home button to take the Strava app off the screen. You'll see the icons of other apps, but Strava will be working in the background. For some reason, this absolutely saves me lots o' battery. I can easily get in 4-1/2 hours of continuous riding using this "trick" alone.

(In fact, I've tested other GPS apps and do the same with them and get comparable results.)