I can verify that Navionics on android requires signal to verify the license. This bugs me too, especially when I am just popping on the plotter to see my location at night. My world is landlocked, and I don't do "planning" like you folks to the phone is my only plotter.
I've tried a couple programs and find the Navionics is pretty stellar for the price.
I will give a try to some of the others mentioned here though, as as best I can tell they are all available for android as well.
I WILL say, that I support smart-devices for my job (again a geek IT guy)... and my Droid Razr Maxx (original) at 2 years old can run for 12 straight hours with the screen on and active overlay satellite imagery onto the screen while doing it, where my old iphone 4 couldn't do it for more than 2 hours without toasting the battery (I doubt the 5 is much better).
Beyond that I think it's amazing what can be done with smart phones, and tablets now. I think with time (and some standardization in size of tablets) some really great cases, mounts and the like will make them default Chartplotters for everyone. I mean it cannot be far off since the FAA already allows ipads for Pilot charts (2 years ago) FAA OKs iPad for Pilots' Charts | Autopia | Wired.com
The Lifeproof cases also work well for protecting/weatherproofing these... as does Otterbox.