Would it be possible to have a section in Garmin connect to see battery usage of the watch ?
I am afraid that not. At least not without redesigning the firmware on all Garmin's models. AFAIK, the devices currently do not send any such information to the phone, hence the phone app cannot display it. You can suggest it to Garmin, though - they may perhaps consider it for the future generation of their devices: Submitting an Idea to Garmin
There are some apps in the Garmin connect IQ store for the watch itself. I use and recommend Battery Widget: apps.garmin.com/.../a9c9b981-1f4c-4399-a270-7d6c7317893e