They were sold as a pair with battery. They've been redesigned so the ones in the link are the updated version. I don't know what the improvements are. But I imagine they can only be better and mine work great.
Gas powered edger and blower are more powerful so it just depends on what a person is going to use them for.
The 18v battery powered Ryobi tools work great. Definitely better than string trimmer/edger with cord. I hate those too.