Some badges can be obtained only by using a device with specific features.Precisely.
badge gravel ride how to get?Acquire, register and use a Garmin device model that can record timed activities with a mountain bike profile, or wait.
Some badges can be obtained only by using a device with specific features. I'm not sure about the gravel badge, but it's possible that you can't have it with your 645.
New to Garmin devices. Just got Fenix 5s, found i could add MTB ride (and walking rather than tracking my commute as a 'hike') to my watch through the Garmin Connect App by clicking on the watch at the top of the app and selecting 'Activities and Applications' but no option for Gravel ride.
Had a thought but not yet time to try it out - create a route as a gravel ride on the Garmin site. Save the route to your device and then activate it when you go out. This may force it to log the activity as a gravel ride rather than just a bike ride.
Login on connect.garmin.com.
On the left shoot out pane choose "Activity" or similar (sorry - translating from Danish and don't know the exact wording :-) )
Schroll down to your Mountain Bike activity and select it by clicking on the headline.
Once you are in the overview of the activity. On your upper left - left of your name - there is a small triangle. It is a drop-down, which let's you select a number of activity types.
Click it and schroll down and select "Mountainbike". Voila. You now have a Mountainbike activity, no matter which unit you have recorded it with :-)
It works for a lot of other badges too :-)