Originally Posted by joejack951

I use a dedicated cyclocomputer (an old Polar HRM) on my handlebars and keep my phone in my pocket running Strava. A 50 mile ride drains the battery maybe 30-40%. I always have it fully charged before doing a ride of any considerable length so that's no problem for me. I may pick up a small spare external battery for century or longer rides but those are few and far between these days.

As far as accuracy is concerned, my phone and computer report mileage within a few tenths of each other at worst. That's good enough for me.