And glitches do happen. On both the HNL-NRT flight (a 747) and the NRT-PDX flight (an A330), problems with the on-board entertainment system obliged them to do a "hard reboot" of the on-board entertainment system, which apparently runs the power to the seats as well. This takes roughly twenty minutes. On the A330, I was amused to see the reboot code running on the screen at the front of the cabin -- apparently it runs on Linux.
I had sufficient batteries -- four of them -- that I could have probably stayed up for the entire flight, but Lisa had only two, and the game she plays uses a lot of power because it wants to run the CD-ROM continuously. Had we networked the two machines together as planned, it would have been worse. So she shut her machine down after an hour or so and did what she could to pass the time. She then switched to the other battery for the last 90 minutes or so before the breakfast service.
I note in passing that the instructions in the in-flight magazine say that NWA's 757s have 200-watt power supplies, which is more appropriate for the demands from our computers. I reckon the power supplies on the 747/A330 are okay for running smaller devices like iPods and such, but not for most modern laptop computers.