iPad Mini 2 - “Hey Siri” won’t respond with a power source

Is the iPad Mini 2 a device that can activate Siri without a power source? Before iOS 12, I thought I turned on the option to only have it listen when plugged in, but I guess I’m mistaken because I cannot turn it off. There is an option in settings to have it listen for “hey Siri” but it doesn’t work while turned on.