Edge 20/25 look to have shorter battery life than the older Edges – “up to 8 hours” claimed. The 25 will certainly be less if using bluetooth.
fwiw, I used my 810 to navigate me the 10 miles to the start, then had live tracking (uses bluetooth connection to phone for uploading the data) going during the 6 1/2 hours it took me to complete and it was on 41% battery at the finish. My iPhone 6 was on similar battery by the end too.
Fundamentally it’s choosing:
– do you want bluetooth for live tracking / uploading via your phone?
– do you want navigation with maps?
– do you want to pair a heartrate monitor?
– do you want to pair speed, cadence, power meters, etc?
Budget goes up and up depending on how many of those you want.
I should really knock up a flowchart, I’ve had a couple of mates asking similar recently.