I'm interested in using a laptop battery as an external battery pack for phone As title said I'd like to use a laptop battery for my phone as an extender.  One usage would be on a plane where my laptop is too bulky to really use but I could pull the battery out of it and use it to keep my phone battery charged while watching movies and what not.  It seems like I should just need a 7805 voltage regulator either linear or switching.  Has anybody done this or thought to do it, it seems like it should be fairly straightforward?
Many laptop nowadays supports charging over USB while sleeping/suspended. So you only need a long USB cable, and put your laptop under the seat in front of you in sleep mode. A 1.5m cable is best but 1m would work as well.