Lots of great suggestions for external batteries.

I bought a battery/panel charger, but frankly, the little panel doesn't deliver enough juice to be useful. The battery is good, but unfortunately it shuts itself off and won't do a float charge. Watch out for the auto-off "feature".

I very much dislike my Android style chargers, and think the cords and charging ports are very much vulnerable to damage if trying to use them when riding. I think the Apple chargers may be a little more robust.

An internal extended battery may be available for many Android phones, but not necessarily for Apple phones. Still, it is worth looking for a semi-integrated extended battery.

I use my Android phone for route recording and mapping. But, if doing 100+ miles, I'll set my screen time-out to 30 seconds are so (or manually shut off the screen), so open the screen, view what one wishes, and immediately shut it back down. Thus, just use the map for critical turns.

I haven't used MapMyRide. But, Strava has decent free mapping software, but has one issue that it likes to forget one's route if one hits the wrong button.

RideWithGPS charges for the mapping features, but has good speed tracking functions. One benefit of RideWithGPS (on Android) is that it has "Handlebar Mode", which allows you to click one button to re-activate. But, it also has the issue, that an accidental activation of the screen could drain your battery without you noticing it.

I keep intending to configure dynamo wheels on a couple of bikes for both lights and auxiliary charging.

There is a Busch & Müller USB-WERK designed to take dynamo power and create USB, including a cache battery.

https://www.peterwhitecycles.com/b&musbwerk.php