Considering: battery + terminal hardwired thru relay coil thru BJT back to - terminal
Your circuit diagram is weird, it looks like you have shorted the battery with the relay. And the USB (power?) to the RPi I'm assuming is not being cut by the relay. You have some other load connected to the relay? Anyhow the current through the BJT when off would be in the nA range. You should add a freewheeling diode to the transistor also to not blow it up when turning off the relay coil.