820 Battery life on cold days & in general.

Same here! I got the same problem... after six hour ride the battery is only 22%left!
It was not like this ... garmin says 15 hours but in the real world I used to get like 10 hours of riding but now in one ride I dry out the battery specially if you are following an track.

I've found that cold & navigation have the most impact on battery life. Particularly the latter - 8-10h ride in summer with mapping/navigation pretty much runs the battery to 10-20%. Recently 4.5hrs in 0C used up around 60% of the battery with navigation on. More frequent data recording, redrawing the screen and communication with all manner of sensors also uses up additional power. On the other hand you can turn on battery save mode which turns off the screen unless touched, saves a lot of energy. Haven't tried ultra trac yet - 50hrs claimed.
Ultimately I think garmin scrimped on the battery size and CPU power to keep the size the same as the 520. Nothing wrong with that per se, it's simply a design decision that results in a trade off. Personally I'd accept something between the 810 and 820 in size for a boost in battery. The 1000-series is just too large.

I'm not sure if this is only due to the cold weather, but I experience battery drain nowadays too. After about 2h ride the battery drops to 50%, without navigating. I only use a ConnectIQ app to display heart rate graph. I have also paired speed, cadence and wattmeter sensors on other bikes that I do not use now.

hmm.. my 820 is about four months old. i have cadence sensor, hrm, and glonass.. but i have noticed that it eats up battery fast. perhaps it will be drained in like 4-5 hrs... any tips on how to prolong the batt life?

Mine was one of the first ones 8/2016 and the battery life is still great. Strava says I rode 474 hours last year so you could probably add a bit for how long the Garmin has run in 2017 alone.

Even accidently leave it on occasionally after a commute home at night (7pm), get up the next morning to ride to work and find the Garmin still on... still about 35% battery left, easily enough to get me my 2.5hr return commute without shutting down. I don't run any ANT devices and have used navigate about twice since new.

My 820 is about 8 months old now and I have also noticed the battery is draining quickly. Its only started over the past month or so. But now a 3 hour ride and the battery is dropping below 50%.

I started noticing the same battery life issues the last month. I have had mine from 9/2016 and battery life was good when new but I did a 5 hour ride today without NAV on and it was down to 11% (started fully charged). Maybe something in the 8.7 or 8.8 update?

It definitely must have something to do with the soft updates. Just after I purchased the device (Jan, 2017) the battery life was at least 2 times longer than it is now. I am really looking forward to having the issue fixed with the coming updates. The battery life is the most irritating issue with the device. Any comments on that from the Garmin party?

Mine ok - no problems with battery life.
If I were you I'd contact Garmin Support - They might have a solution or fix it under warranty.
I allways find them very helpful.
Nick

Alright, I'll have a try. I have just written to Garmin Support using the online form.