Yeah I've run them on 40's.

At that price I'm also considering purchasing about a dozen of them and using them two to a plane ( you can hook up two via a "Y" cable! ).

This will double the capacity, but the batteries would have to be charged separately outside the plane.

Remember that at 6v a single pack will last about as long as a 4.8v 800mAh pack neither of which is bad, but I prefer to be able to get 14+ flights in on a good day at the field!