I went with a garmin 1030+ few months ago because of the battery life.
It will easily handle 300K brevet using a HRM and a varia radar.
At the end of a 400K (21h total time) I still had 70% of battery life in energy saving mode (screen turned off until an alert comes up or the screen is tapped). I only had a HRM, no other sensors linked to it.
No experience yet on how it handles longer tracks.