ultra trail run and modes

PhilFrance said:

Do you have any advice to keep my Garmin instinct alive for a long long time during a trail run ?

You could try the Utra Trac mode (www8.garmin.com/.../GUID-AFF93BBA-2F68-4C2A-9667-DE3168B3C49C.html ), but the resulting track is rarely usable, often full of inaccurate positions at indvidual key points (the sampling rate one minute). You can also take a powerbank with you, and charging it it every few hours, though i am not sure whether it is doable in your case.

You can also use a Heart rate strap and also save battery on the watch. Using a small power bank as Trux suggested seems the best solution, as you can charge the watch many times even with a very small one.

darnich said:

You can also use a Heart rate strap and also save battery on the watch.

Yes, good idea, but I am fraid it would not help much in this case. The consumption of the HRM is negligible in comparison to the GPS, and I fear there is no chance to keep the watch running 54 hours with GPS on. The specs tell up to 16 hrs in GPS mode, and up to 40 hours in Ultra Trac mode. Shutting down the HRM may perhaps add a few minutes or an hour, but even if the watch were set to the Ultra Trac mode, and paused for some sleep periods, it would still be quite on the edge of its limits, so I would be afraid of losing the data, without recharging it.

Recharging the watch is an absolute must. I'm just saying that  by using a heart rate strap he might save some valuable time before he reaches the next refill station

Many thanks for all your answers

I may try to use a little powerbank during my training (weight is the enemy :) ) Pause, using the powerbank during this timelap, continue my trail and so on. 

PhilFrance said:

I may try to use a little powerbank during my training (weight is the enemy :) ) Pause, using the powerbank during this timelap, continue my trail and so on. 

Just make sure to test it before the real run - I never tried recharging the watch while the activity is still running. Hopefully the activity won't get interrupted, deleted, or otherwise interferred with. You better try it now, than finding it does not work during your ultra run 

''Shutting down the HRM may perhaps add a few minutes or an hour,'''

You greatly under-estimate how much power the HRM uses. In my experience it reduces battery in an Instinct by c3 hours. 15-16hours with GPS and 11-12 with GPS & HR is about right. On my previous watch the HRM reduce battery life by about 20% as well.

Powerbank worked for me when I tried this out, obviously you temporarily lose HR while it is charging (I took the watch off).

That's why I suggested a heart rate strap in my previous answer. HR data will come from the strap + the watch will consume a bit less battery by not using the wrist heart rate

I got a little tiny (3,500mah or so) battery pack that only weighs about 3 ounces, that I take backpacking with me in case I need to recharge the watch mid-trip. It's good for 5-6 full battery recharges, and is shaped like a thick credit card. Might be a good option for a runner. I think it was like $12 on amazon