Battery life is always a real concern. Most of us with a dedicated cycling computer like the facte that just a glance allows us to see what or stats are. We do not want to have to touch something to make it visible. Even at very low brightness settings, forcing any smartphone to display continuously is a huge power drain and on any longer ride the danger is always of shutdown and loss of all the data we have acquired. You are powering both the phone and the Wahoo attachment.

I have always felt that a dedicated cycling computer is a better solution than a smartphone even though I do carry my phone on every ride. This is especially true on long rides.

A suggestion for your old phones, if you are in a financial situation to take advantage of it, donate your old smartphone to a battered women's shelter and take the tax deduction.