Battery life - unrealistic expectations?

So I went for a 3 hour bike ride on Sunday with a fully charged 935. At the end of the ride the battery was 80%. So that's a 20% drop in 3 hours. At that rate, the battery would only last 15 hours in GPS mode. I thought it could last 24 hours?

To note, I had it paired with a HRM-Run strap, had GPS + GLONASS enabled, with 1 sec. recording, and 100% backlight brightness. Even so, it still falls significantly short of the expected battery life. Not that I ever do any activities lasting anywhere near 15 hours, but still.

100% backlight ?? mine is 20 or 30% and it's OK (for me) have you tried it ?

I think I lost 40% after a 7h ride with my HRM + GPS+Glonass (1sec) + power meter + cadence sensor + speed sensor + bletooth ...

I was pretty impressed because for the same ride the EDGE 1000 finished with 1% battery ! (but I used it for navigation and livetrack) + the other sensors

If you want to save battery but otherwise record a normal activity then using GPS only not GPS+GLONASS and not using the backlight are easily the biggest battery saving measures you can make.

Whatever battery claims are made would be almost certain would be without using things that drain the battery a lot that you don't really need.

And yeah 100% brightness? Did you have the light permanently on?

Just from my own usage in 24/7 mode 100% backlight on auto and 50% backlight with gps+glonass for everything (other than indoor workouts) with 5-6 days a week of work (totaling in at around 20-30 hours of recorded work in that way) and I can hit the 50% mark in about 4 days, give or take a day or so. I personally think the battery life is good on the watch, but where I am actually really happy about is how fast the watch charges.

Normally I just plug the watch into my computer to let it charge and dig out my adopted vivosmart hr to keep recording going (which true-up does work...mostly). When I had my F3HR and later the 5X and 5 at around the same battery life, i'd have to wait 1-2.5 hrs for it to charge. This Forerunner gets to 100% in less than an hour. I counted 37mins to full from 51% on Sunday (last time I charged). two days later and a 40min run yesterday i'm sitting at 86%.

As I said, for me the watches life is really good and the charge time is as well. Play with the settings if you're draining quickly. Perhaps disable the backlight in sport mode? If you're outside a lot for workouts, you might not need it. I don't either, but i've gotten so used to it now, I just have to keep it on, it bugs me if I turn off the backlight while outdoors.

Eh, 100% brightness, 1sec, gps+glonass?

I'd say 20% in 3 hrs is pretty decent then... Turn down brightness (hell, I have it on 20 or 30 I think which is plenty) and gps only and/or smart recording and you get more in the expected ranges. Advertised numbers are always in optimal surroundings and with everything set to the least power consuming mode

I thought it could last 24 hours?

Battery life is "up to 24 hr. in GPS mode and wrist-based heart rate" in activity mode page 26 of the user manual. Specifications do not state 24 hr, just imply that it is possible.

Read page 29 of the user manual for tips on how to extend battery life.

i agree with what everyone else has written above. while i don't consider your numbers all that bad considering the backlight being at 100% and GLOSNAS+GPS enabled.

in my experience, i find GPS (1sec)+oHR consumes close to 5% (a little less) per hour which would project to about 20 hours. (my default backlight is at 20-30% but i dont know if that's on when i'm doing a GPS activity since my runs/hikes have all been in broad daylight)

i also use my watch a lot using a chest strap. just this weekend i did a hike of almost exactly 2 hrs and it used 7.96% (according to a battery gauge widget) in 1:58 minutes. so that gets close to the specified 24 hours.

Would do the same ride again after changing one or two of the mentioned options to see what happens. I'm very satisfied about battery, did a (shorter) bike tour yesterday and have 70% battery remaining even I am using a (self made) connect IQ datafield which does quite a lot second by second.

And a feature request to Garmin: please allow 15% and 25% background lightness, this would be great!

I have the brightness set at 100% because I find the screen easier to read at this setting. I do the same with my phone. I could lower it to 80% but just prefer it set to 100%.

Even with all the senors turned on and a bright screen I am still happy with 15 hours, but know what I need to do if I require it to last longer between charges.

Fair enough and every right to do so of course, but then you shouldn't be surprised that you don't reach anything near the 'max up to x hours'