Livetrack drains Iphone

Are you riding in a area with good cell phone coverage?  If the cell phone signal is weak, this will increase the drain on the  phones battery

I would say yes coverage is good, maybe some blind spots short periods of time Riding Mallorca in populated areas. Should the phone be set to 4g only?

One option is to turn off "search for wifi." An SE probably will not have enough battery to last 12 hours regardless of what you do. 

Perhaps connect your phone to a powerbank to keep it charged during your ride.

I recall that previous Edge units stopped searching for Wifi when a activity is taking place. Why has this been changed on the 1050? What would the purpose be of connecting to Wifi during a ride?

Turn off livetrack or use a power bank to charge your phone

Turning off "search for wifi" is an option on the iPhone SE. I do not know of an instance that the 1050 continually searches for wifi during an activity. I might have misunderstood your point.