Even the entry level Garmin (Garmin200) lasts long enough for a double century. Where I ride a smartphone will only sometimes just barely make ti through a metric century, sometimes not even that. I now use a Gamin 510 with my smartphone linked to it. There are some nice features with this setup and long battery life for both devices. An added bonus is I still have a phone when or if I need a phone.
__________________
Sir Mark, Knight of Sufferlandria