I use the electrovaya pp120 and it can crank out about 5 hours with the screen on and powering the interface with Phantom. I picked it up off ebay for $80 shipped and it works for my purposes. BTW, I have a fujitsu laptop (b2175) and the extended life stock batteries can be found dirt cheap. I have a half dozen of these and hot swaping with the electrovaya, it can do about 12 hours total record time.