I don't think he's talking about a battery that lasts 7 hours. Just one that works for 15 minutes in a 'minimal use' mode. You know, brightness minimal, unused wifi/Blutooth shutdown, automatically stop playing media content, eject disks and other drives and tell the user he has 15 minutes before the computer will power off.
Apple does provide a way for you to use the secondary display as the primary monitor, just go to System Preferences --> Displays, click and hold the white bar above the first blue screen, then drag it to the second one. It's not idea, no, but it works.