Battery Saving Conservation Measures During Ultra

The biggest power drains are GPS and backlight. OHR is next on the list, but it is WELL down on the first two.

GPS. You've made a compelling argument for keeping it at 1s. As the nominal rated life is about 24 hours with 1s GPS running, that is too close to want to do without charging along the way (I don't know about you, but I'd be gutted if I ran for 24 hours, only to find I missed out on recording the last hour because the battery died).

Backlight. Each 10% backlight drains about 1.5% of battery per hour. As you will want to refer to your watch overnight, I'd suggest Gesture, After Sunset with a 4 or 8 second timeout, and at just 10% intensity (or even 5%). If you were referring to your watch every 2 minutes for 12 hours of darkness, this would represent less than 1% of battery capacity. More generous assumptions about backlighting for navigation checks at night would still mean less than 5% consumption over 24 hours. At higher intensities, backlight could put a huge dent in battery run times. Also make sure you set an alarm sometime after dawn to remind you to check the BL is now off (a mistake I made on a 15 hr bike ride).

OHR. HR benefits include training load, recovery, pacing on varying terrain (which might be harder at night without visual cues as to how steep it is), and calorie burn (if you are using that to guide your fueling strategy). The quoted run time of 24 hours includes OHR on. It's not a huge battery hog - I guess maybe 10% of battery over 24 hours. Using a chest strap or Sosche would give you (better quality) HR data without OHR.

Other: Activity tracking drain is pretty small in terms of GPS, backlight, etc - it might be noticeable over several days, but not so much over 24 hours - personally, I'd leave it on. Rather than messing around with notifications, I'd just turn the BT phone connection off at the watch. Recording interval is about file size, not battery consumption. You may also want to check and test any Connnect IQ data screens - some of them may be more power hungry than others.

Charging: With the length of the event pretty much at the nominal GPS run time, you will probably want to have a battery charger anyway regardless of other battery saving measures, rather than risk not recording the final stages of the event. Only if you are willing to use Ultratrac should you forgo a charger. If you are having to carry a USB battery and cable, you might as well use them. It charges at around 4% every 5 minutes. You could charge for 5 minutes at each food station (I'm not sure how they organize these things at 24 hour events), or you could hang it off a caribeener for a while (and sacrifice HR data for that portion). Basically if you can get 30 minutes/25% charge into the watch along the way, you should then be golden to make it home comfortably even with OHR and some moderate backlight use.

Good luck for your event!!

How long is the loop that you're going to be traveling? Have you run the route before and done any preliminary testing using UltraTrac?
I really only ask since I've done a lot of UltraTrac testing and have been very impressed with Distance Accumulation. If your primary concern is battery life then I wouldn't dismiss using UltraTrac. To the contrary, I would recommend it. The longest event that I've recorded was just shy of 34 hours (with a Fenix 3) and the battery level was at 11% at completion. That was using 1 second recording although I typically only using smart recording. Test included some static sessions so isn't necessarily relevant in declaring battery life expectancy but the Fenix 5 should certainly be able to record a 24 hour event without issue.

Thanks for the great feedback - exactly the input I was looking for. That said, I will probably: use smart data recording, backlight during activity - alerts (and maybe keys) after sunset, 4 second timeout, brightness at 5% (I'll research gesture as I've never used it). I'll also keep the OHM and activity tracking on but make sure the Bluetooth is turned off, and I'm using a OEM watch face.

Since the loop is only 2.25 miles and about an hour drive, I'll try an Ultratrac comparison tomorrow - great idea. Thanks again for the feedback - I'll update as things develop.

PS "Gutted" to say the least ;)

UPDATE: so deeter26_2 and mcalista - I ran the loop of the Ultra this morning comparing normal to Ultratrac (see links below). The Ultratrac "straightened" two stretches on the NW portion of the loop and one in the SW. Overall, it resulted in only 0.05 miles more using Ultratrac for the loop. That would only be 2.04 miles to the plus over 24 hours since I'm shooting for 100+ miles (please check my math: 102 miles / 2.5 mile loops = 40.8 loops X 0.05 miles difference = 2.04 miles).

Since I'll be passing the official timing station every 2.5 miles, I think the pros of using Ultratrac (not worrying about battery life or charging on the go) will outweigh the cons (minimal mileage difference) since I can always double check it each loop. Thanks again for the feedback, I really appreciate it.

https://connect.garmin.com/modern/activity/2563694730
https://connect.garmin.com/modern/activity/2563694089

That's pretty great results using UT. Your accelerometer must be tuned pretty well! You could calibrate it for increased accuracy but I don't know that I'd bother. Just for fun, I used the UT/Smart settings for a road marathon today and didn't do quite as well. The F3 doesn't allow manual calibration however so I didn't really expect it to be dead on. I finished at 25.2 so lost a mile but that didn't really faze me. It seems to perform better when I'm in the trail and I also think that compromises the road accuracy a bit. I'd be really happy to see a .05 distance variation over the loop that you ran.

Did you have activity tracking on during your testing? How did the battery performance stack up?

Good luck on the 24 hour!! That's next level stuff and super impressive.

UT won't affect the behavior of your run/walk alerts but a run/walk action plan could affect the distance accumulation results of your event. I've never tried it but I seem to get the best results when I'm using a more consistent arm swing. For that to make sense, you have to understand the basic principals of UT. GPS runs through 2 minute cycles. It's active for 20 seconds and inactive for 1:40. GPS is used as the distance source while GPS is present and the accelerometer is used as the distance source when GPS is inactive. A run arm swing and a walk arm swing can give you varying feedback so would impact the end result. Some people assume that distance is calculated by connecting the GPS dots when it's on/off but that is certainly not the case. Did you run/walk during your test run? I'm guessing not. Again, I'm really comfortable with UT but I've never had it out using run/walk. That said, I'm also comfortable using a charging bank so if push came to shove I'm not sure what I'd do for a 24 hour event. PROBABLY use a charger on laps 20 and 30 and run straight GPS. How's that for hypocritical advice. HA!

Marathon was great but a very hilly course so legs are pretty beat up! I was a pace leader for this one so more sand-bagging than racing but it still did some damage. Ouch!!

Ugh - now you've got me second guessing myself. I might need to make a run to the local electronics store for a smaller charger!

There will be pros and cons with whichever method you select. Ran an ultra with friends in a snow/ice storm where it was 15 degrees F. Was using GPS On. The transition zone was a shelter with a full on chili bar and fireplace. We had several extended pit stops and being inside a shelter for 15 minute stretches added quite a bit of artificial distance. Didn't give a hoot about that. Remember that day as a great sufferfest with friends and have no recollection of what the watch readout was that day for distance. I'd have to go back and look it up. I think the point is that if you expect that you'll get an absolute confirmation with your official race results (distance covered) and your Fenix 5 then you'll probably be disappointed. Even standing still in an open area during transitions can accumulate distance. I would expect some variation and then be greatly impressed if that delta was within your expected tolerance level.

Let's say that you're moving through your laps and maybe taking an extra 10 minutes every 5th lap or so for nutrition. Even putting your watch on a power bank for those periods should suffice and then you wouldn't even have to charge on the go. That's just another thought.......

Last Sunday I ran 48,5km in 5:46h as preparation for an upcoming 100km in two weeks.
My fully loaded F5 with lights on during activity (20%, 8sec, gesture), intelligent recording, Bluetooth connected (forgot to turn it off) and DozenRun as datafield went from 100% down to 66% in those almost 6hours.

I´m taking a 10.000mah USB battery for my Android mobile with me and just to be on the safe side the F5 charger cable, but I´m aiming at 13hours and the F5 should be fine.

so in my usecase: 6hours = 33% = less than 18hours

EDIT: never tried charging on the run so far, will do in advance. I´m wearing a Salomon ADV Skin 5, so there are pockets in front for storing the charger + watch during charging. Will use breast HR, no OHR