FW 12.1 battery drain

I too am having this issue. Max battery life is now about 6 hours. I'm using garmin support to find a solution. I'm not hopeful! But basically so far all they've said is "there is no known problem with this device, can we have more info please." Sent them a link to this forum and they just said people like to complain on forums. Anywho, I'll keep you updated if they come up with anything helpful. They are at least replying so far which is a start. 

Yes, you have to wonder if Garmin has made the same decision as Apple, to incorporate software changes to older models, that makes thing slower or intentional use more battery. Just to make us buy new units.... 

Have been following this thread hoping that a resolution would been found (other than reverting back to FW 11.20).  Finally called Garmin, who verified that there was a case open on this issue.  Sent my files from my 820, so will see what kind of response I get.  Was using the 820 with my Wahoo Bolt simultaneously for a different reason and show a 15% burn rate per hour for the 820 compared to about 8% for the Bolt for the same ride (they were connected to different powermeters).  If Garmin can't resolve this issue, I will be buying a Roam. 

That's interesting, I was using Garmin support via email and they told me there is no known issues relating to this device and battery drain! They told me to send my 820 back and they will send a newly overhauled device to me. Havent completed the online form yet but i will send it back, then update to 12.1 and see if it has the same problem. My guess is that it will but maybe then they admit its firmware related

Just an observation, my 820 discharged very quickly as per every one else’s experience on this thread. Right down to 3%. But.....it then continued to work for a few hours more? Wondering if it’s not battery drain but a misreading of remaining charge causing the prob (potentially both of course?).

I've mentioned in other threads that we don't know the actual battery level, only what the gauge shows, unless we time it until it shuts off.  Determining charge level for Li-ion batteries is tricky because the voltage slope is very gradual and changes over time.   I've had other devices showing low battery capacity where letting it run until it shut off recalibrated the gauge which then indicated charge level more accurately.   IDK if this recalibration applies to the 820 or not.