Ryland did a great job of covering the question. Since you've said "twice" twice though
let me just add that doubling your battery pack size probably won't quite double your range. If you were just running an electric motor with no load, yes. But the motor you're running has to move those batteries, so as you add more of them the weight goes up and you get a "diminishing returns" situation.
How much you fall short will depend on things like the ratio of battery weight to total loaded vehicle weight, and the shortfall may be so small you don't even notice it, but it should be there.
This is just an off-the cuff thought, but maybe: Find out what a second battery pack weighs. Load that much weight into your vehicle. Drive it and determine the range/time with that load. Double that value and that might represent what you'd get with the second battery pack, presuming the condition of both packs are identical. (Anyone see a fault in that thinking? I didn't ponder it long so I don't have a lot of confidence in it.)
Of course if you go with lighter or higher-energy-density batteries, all bets are off.
Not quite making "twice" aside, I like that you're thinking along these lines. The more of us pondering creative approaches to FE, the better the chances everyone will benefit.
Rick