If you're in economy, there isn't one port per passenger even if you're in a port-equipped row. There's one between each pair of seats: one in a two-seat row, two in a three-seat row and so on. If everyone in a row wants to use them, you may have to work out a time-sharing arrangement with everyone using their battery part of the time, run a cord to an unused port in front or in back, or (passenger load permitting) switch seats. I've never seen this create a problem but it's something to keep in mind.