Before I replaced my Garmin I rode for a couple of months with the Strava app and an iPhone. Never had battery problems and my longest ride was 7.5 hours. (It was an iPhone 5 or 6.) The only difference between the Garmin and iPhone for me was, of course, the lack of cadence or HR on the iPhone. However, all other data was accurate although the algorithm estimated power varied between the Garmin and iPhone for the same ride and or segments. Overall the iPhone tended to show more power. However, the Garmin has always been clearly wrong on estimated power for descents. It way underestimates.