On Wednesday, September 9, 2020 at 7:37:17 PM UTC-4, wrote:
I wonder how much of a current draw the bluetooth feature is.

The Bluetooth feature in the battery is BLE (Bluetooth Low Energy) and works by sending out small packets of data every few seconds. The infrequency of these transmission results in a very low overall current drain, probably on the order of 10 micro amps.

The phone app "listens" for these pings and can make a connection to the battery. While that connection is held, the current consumption typically goes up to the 10 milliamp range. These connections happen when the user uses the app to check the battery status. Eventually the connection is broken and the current consumption reverts to the 10 micro amps.

When the app is active on the phone, it has to constantly scan (listen) for transmitted packets so the Bluetooth is on and consuming energy from the phone battery. So yes, the phone battery is affected when the app is running.. After the app goes into the background the phone operating system typically suspends the BLE scanning so the current consumption due to the scanning goes away.

Danny Brotto