This means that one can keep running over multiple days on a stage race without charging the Garmin fēnix™ or do a 100 miler (that takes the average runner upwards of 24 hours) and keep an eye on the data you are recording the whole way. Not being an ultra trail runner myself I have only tested the Garmin fēnix™ over about a 5h30 trail run, so cannot really comment on the actual battery life achievable, but it seems to be pretty close from what I’ve heard. However one does need to understand the technology behind attaining this battery life from the Garmin fēnix™, namely the sampling rate.
Sampling rate means the time taken between the recording of GPS coordinates while trail running. The longer the sampling rate the longer the battery lasts as the GPS is used less (and vice versa), but your distance and average speed may not be accurately recorded if you are running a twisty trail like a switch back. This is because the GPS coordinates will be relatively far apart if you are going at pace, and when they are connected to form your route and calculate your pace they take an ‘as the crow flies’ approach so you end up with a more direct route down the mountain instead of the actual curvy one that you took.
If however one would still want to use the normal one second recording mode while trail running, a good tip is that the Garmin fēnix™ can be charged while still being used and worn by connecting a mobile USB battery pack (like the Garmin External Power Kit) via the USB charging cable.
Besides the extended battery life, navigation is the other distinguishing trait of the Garmin fēnix™. Firstly the Garmin fēnix™ plots a bread crumb type route of your running activity while you are running. This is visible while trail running and allows you to orientate yourself on your current route. One can then mark a point on the route to navigate to at a later point or you can use the TracBack feature to invert the course for you and get you back to the same place you started via the same way you went out. This makes it ideal for out and back trails, but less ideal where the starting point is significantly closer than going all the way back as the Garmin fēnix™ understands point to point navigation, but not any form of routable navigation like those found in cars.
Other than navigation on a trail run that has already started, one can also navigate on a given course or to a given waypoint. The easiest way is to have the routes created via Garmin Connect/Basecamp first and then uploaded to the Garmin fēnix™ before you start trail running. You can also add them later on the Garmin fēnix™, but adding any other location beyond your own is time consuming when done in this manner. Once the route has been uploaded to the Garmin fēnix™, you’ll be able to run it, view an overview of it, edit it, or reverse it.
The navigation screen will come up, where you’ll see the distance to the next waypoint within the route, as well as the estimated time it will take to get there. Telling you which way to go is the job of different data screens, presenting the same data in multiple methods. The outer ring of the Garmin fēnix™ acts as a compass with the two little stripes on the display’s edge telling you where to go. You simply point yourself in the direction of the stripes and run! There is also a compass view, which can be shown with degrees instead of just textual directions. Then, once you reach a waypoint, the Garmin fēnix™ will automatically switch to the next waypoint in the route and so forth. One can press the red button on the Garmin fēnix™ while on the map screen to zoom and pan the map (Note when I talk about map here, I mean a breadcrumb route not a Google Maps type map). Lastly the Garmin fēnix™ includes a magnetic compass, which means that it doesn’t depend on GPS or movement to tell you which way you are facing.