Check Hybrid System 2010 Prius

There's an area on the connector you have to squeeze to release a latch that holds the mating parts together. Disconnecting allows putting the bracket completely aside so you don't have to deal with the wire and bracket while wrestling with batteries.

 

Leave the hood popped, all door's closed, and fob away from the car: it'll be very close to nil load. I did a load test under those conditions, it was infinitesimal. In short, you don't really need to remove the battery from car to check it's voltage.