820 is losing battery on short rides. Here is my ride and garmin 820 had 3% left.
You should have my file. I have the latest update 12.70.
Unit ID 3966449429.
Looks like you're trying to contact Garmin Support. This is a users' forum and not Garmin support. Go to the Garmin website for your country and scroll down to the bottom for contact info.
FWIW, the 820 never had great battery life to begin with, and after some years of use, the battery capacity decreases further. You might try leaving it on until it turns off, then charging it. That might help a little. In my case, I connect an external USB power stick for longer rides.