Board Thread:Questions and Answers/@comment-101.53.203.101-20180615072204/@comment-17964257-20180615105511

Batteries. NerveGear units have batteries to keep the device run safely in case it's cut off from the power supply, as explained in the Light Novels, as well as in the anime.

As for the Ethernet cable, once again, as was explained in the Light Novels, as well as in the anime, there was a period where tons of people lost their connection to the servers in the game. This is assumed to be when the players were being transported to hospitals.