I've just got an active 2 and I'm assuming I must be doing something wrong, I'm seeing 24-48 hours being quoted yet I'm lucky to manage 12.
Mine is the 40mm LTE version
WiFi and 4g set to auto - phone is connected by Bluetooth most of the time
Low intensity vibrate
Watch face always on- off
Heart rate every 10 minutes
Brightness quite low
If I lower the settings any more I might as well not use it, what am I missing??