I would like to show Android phone (connected with tizen gear via 'Samsung Gear') battery status on my Gear S3.
My web application, can access watch battery status via navigator.battery. How can i access phone battery status?
Right now, There's no Tizen API/function to fetch Battery status of Companion mobile device. (Jun,2018)
So you can't show 'companion mobile battery status' using a function call or something like that.
If you really need this feature now:
As a workaround, You can develop an Android app and retrieve current battery level (relevant Guide). Then send the data to Tizen gear using convenient communication channel (Bluetooth, HTTP).