Can you plug in a laptop on a plane or are you entirely dependent on battery power for the whole flight ?

I believe that one is able to plug in on business class and first class on some aircraft however, I've never seen plugs in economy on any aircraft nor have I hear of such.

You would need to check for the specific airline and aircraft -- I'm pretty sure that they are not universal but only on select flights. And you may need to purchase a special adapter -- it's not a normal household type plug. I have seen the adapter kits for sale in computer departments at electronic stores.

You might want to check SeatGuru.com. They have seatmaps of the various aircrafts used by airlines. You'll be able to see what seats have power plugs and what type of adapter you would have to purchase.

SeatGuru
http://www.seatguru.com/

I plug in all the time on AA... even in coach.
The old TWA planes have no power but most the AA planes do, just not every seat.
When you look up, there is a little power outlet symbol on the overhead.
Also, the power box prevents you from putting a roll-aboard under the seat.
You may have noticed...?

Husband who travels weekly on business says it is not just airline, aircraft type or class - it can vary plane to plane. Obviously the newer larger planes increase the chance of having power source available. He has made a connection from one plane to another - same airline, same plane type and one had power source and one did not. (He flies AA, USAir, Delta primarily)