Is it normal for a mobile phone or tablet to drain the remote battery?

Hello there Cerbrus. Good day and thank you for the inquiry The reason why your android mobile device is discharging your DJI remote controller. This is because the Android mobile device needs on-going 500ma to maintain the USB connection, so there is no option for the Android device to disable the charging mode, it is related to the android system and the communication protocol. This is regulated by the Android Open Accessory ( AOA ). Thank you for understanding and support.

Thank you Stephen. Appreciate your help and advice. Newbie to drones. Just learning. Have a Marvic Pro. Wrapped. Thanks again.
Stay safe and fly free.
Cerbrus