Wireless surround can be a snake pit. Not only the technology but the connections. You are correct in that most of them are wireless to the main unit but the sides need to have power and are wired to each other. A battery pack option would be flaky at best.
There are some decent soundbars that will give you much better sound than the tv's speakers, and that my be your only viable option, other than a true 5.1 system (separates).