I have a 1995 Chevy 2500, 6.5L Turbo Diesel. I'm looking for portable power unit (A/C power) to plug the block heater into when I'm hunting for long periods (truck parked deep in the woods). How long would the following unit provide adequate power for the block heater to run?

Amazon.com: Duracell DPP-600HD Powerpack 600 Jump Starter & Emergency Power Source with Radio: Automotive

thanks!