Does anyone know if Course navigation has a big impact on battery life?

There will be an impact on battery life. However, provided you only use the map when you need it, rather than having it as an active page all the time, you should be fine. Of course, you’ll get more battery life with a 7X than a 7S or 7. Which one will you use?

Use this excellent video to save battery https://youtu.be/zLUb9Q2TyhU

Another thing to add to Philip's advice about not using the map screen any more than you have to (it's both the continuous MIPS screen pixel refresh and graphics rendering with the processor that kill battery), but you still want to see the course breadcrumb, is go in to the activity app settings and turn all maps off.  That way there are no battery consuming detailed maps to display/render on the map screen, just the simple power light course breadcrumb view.

Up Ahead shouldn't consume any more power than any other data screen that predominantly has static text on it.

I have a Fenix 7X and used Nav for a 8 hour ultra with map on screen at all time and the odd switch to up ahead and ascent. 
The watch used 18% of battery. I did have heart rate turned off though. 
I’ve got a 100 miler coming up and I have full confidence it’ll last the duration even with heart rate turned on. 

Just got back from a 6.5 hour run and was using courses.  Battery wasn't 100% when I started and was 68% when I finished.  Checked the map a few times but mostly just my main data screen (dozen run) and up ahead now and again.

Lostdotfish said:

Checked the map a few times but mostly just my main data screen (dozen run)

Dozen run is a 3rd party data field. Any kind of third party apps will increase the battery consumption as well. So I recommend to uninstall this data field and use only the standard data fields of the watch.

Agree with that. I only use standard data fields and standard watch faces. 

I've tried but I've been using it so long now, it's hard to ween off it.  It's very well coded (has won developer of the year in 2019) and I've never noticed it cause significant battery drain (on this watch or my FR645)

using a fenix 6x, during 14 hours, in those conditions :

- cold weather (2°c, just above freezing)

- polar h10 (bluetooth)

- stryd (ant+)

- a course set, with mostly the map or climb pro shown

- about 2h30 of night (backlight)

- switching screens quite a bit

- 2 connect iq fields (stryd, and another for time barriers)

at the end, I still had a LOT of battery, can't remember the number, but at least 30% maybe more.

With the 7x, set to max precision, map, course, hoter temps, it was EVEN better !, after 10 hours, I had used less than 30% !!! (a lot of sunlight anyway).

So if you deactivate dual band, or at least set it to change to single band when there is only 5 hours remaining, you'll be more than safe for 20 hours

hope that helps a bit

Crispin_Ellisdon said:

That way there are no battery consuming detailed maps to display/render on the map screen, just the simple power light course breadcrumb view.

The same can be achieved to some degree by changing the map theme to high contrast and reducing the map details level to low. That way the map would still be displayed but fewer pixels would be affected.

In general my experience is that using course navigation increases the battery usage by perhaps 20-30% when not looking at the map screen for too long. I've successfully used course navigation in an ultra that lasted for more than 30 hours with Fenix 6X, and I still had about 30% of the battery life left at the end. The only optimization I used is that I switched the GNSS tracking to GPS only.