Poor battery life

Things to try:

Let it run down until it shuts off.  It may re-calibrate the battery discharge curve.

Turn off wifi and bt if not using it out on a ride. 

Use only GPS satellites and smart recording.  (smart recording may not help if using a PM)

Revert to 11.2 firmware.  That's what I'm running.  I get 5-6 hours with BT active, PM, wheel and HR sensors.  Still not great, but handles all my rides lately.

Thanks. I'll try and revert to 11.2 everything else is the same as yours.

I have a Garmin Edge Explore, on a 4 hour ride the battery goes from 100% to 14%, contacted Garmin and still waiting for any advice on sorting the issue think they are stringing me along. Will be good by Garmin

My Garmin Edge Explore on 4 hour ride goes from 100% to 14%, contacted Garmin still waiting for any sort of help to resolve the issue, think it will be good bye Garmin

Why don't you post and read in the Edge Explore section?! There is a lot to read about battery issues there and even a for may people useful solution as well. Don't throw away your Explore 

I also have a 820 that I've had for almost a year now and has seen regular use. It'll last me ~4hrs if I forget to disable bluetooth, but I recently did an all-day adventure with the bluetooth disabled and it lasted me the entire time and then some. Seems like maybe your battery is bad?