Your Garmin help, please

Very excited to be getting my first garmin, decided on the edge 800.

What's the battery life like realistically, would I be foolish to expect it to be able to use strava and maps for a 100 mile ride?

Lasted the Dunwich dynamo for me and I am old and very slow.

Realistic battery life 15-16 hours navigating.
So if you cannot average 6 kph probably not.