The VR helmets have a battery that can last for 2-3 hours.

I still dont understand why the hero is the only one who can use 2swords when the game is designed to have free character developement (in one episode some random guy yelled that there are no classes in the game).

I've enjoyed this anime as well, but it isn't THAT good. If anything the giant plot hole that you can drive a truck through keeps it somewhat limited in terms of realism.