Is there a way to know if the MG100 is being powered by the battery?

The Canvas Gateway firmware allows the battery on the MG100 to be monitored over LwM2M. The user can know if the battery is charging or is charged, if the device is currently running off the battery or USB power, and the voltage of the battery. This is all available via LwM2M object 3.

This is all done with this zephyr module: https://github.com/CanvasDM/power_module/blob/main/src/lcz_power.c

And is implemented here:

https://github.com/CanvasDM/ble_gateway_device_manager_module/blob/main/src/lcz_ble_gw_dm_task.c#L267