What is a good way to connect rear speakers up by wireless?

I am at my brother’s house and he has a center speaker, a right and left. He also has a powered subwoofer we haven’t hooked up. I’d like to hook up rear speakers, but there is no way to run a cord across the room. What would be a good wireless solution for two rear speakers? Powering the speakers might be a problem so battery would be best, but we might be able to jury’s rig an extension cord. But we have no access to the stereo.