Have you thought of getting a cheap small phone as a bike computer? Just swap in your sim card and leave your big phone at home (unless you're on Sprint/Verizon). I use the Wahoo app on a Motorola E 2015 and it's great. 5hrs battery life (+12 with an external battery when needed) and it is possible to get ANT support as well so it connects to my HRM and speed/cadence unit.