I believe in most, if not all cases there is a requirement for AC power. There is often a BT/IR receiver/amp which needs to be plugged in and then you need to connect the speakers to this, or sometimes the receiver/amp is built into one of the speakers and you plug this speaker in and connect one speaker wire to the other speaker.
In any case, what you're usually trading is long speaker wire from the front of the room for shorter speaker wires between the rear speakers and an AC requirement. Often if you get up and walk between the transmitter at the front of the room and the receiver at the rear you can get audio dropouts, although with some (better) systems the dropouts are rare. Depends on the quality, position of transmitter/receiver and the method of transmission.