I'm very happy with my Edge Explore 2. I ride 100km and some 200km events, and it copes with those with no problem. You probably know that you can maximise battery life on most GPSs in various ways, including only using the mapping screen (which is heavy on updates and therefore battery) unless you need it.
I had an Edge Touring Plus before that (still got it actually, I use it for "light duties"). The Explore is a significant improvement, not only in battery life but also in ability to connect to speed and cadence sensors (if you care about that stuff - it's not that important on Audaxes). There are also more and easier options for loading routes, and it synchronises wirelessly with Garmin Connect (via a phone or whatever). It will provide a track to your loved ones, showing where you are (if you want them to know that!)
The accident alert feature is rather irritating. Theoretically, if you have a crash, it gives you 30 seconds notice and then sends off an alert to your nominated person (again via a phone). In reality, in my experience, it does it when you brake at junctions, or possibly even accelerate hard, which can be a bit annoying for all concerned.