A 500kg battery? Hmm, that's a lot of weight.
All from memory so don't bite my head off;
Energy density of petrol/diesel/avgas etc is about 40MJ/Kg [MJ= MegaJoules]
Best current battery is about 1MJ/Kg, and they are extremely fragile. I would feel fairly safe hitting a fuel tank with a hammer - do it to a lithium-ion battery and it will catch fire. Most battery advances seem to be based on ever finer manufacturing techniques, literally nano-technology, and presumably more fragile. It would flying around with a tank of nitroglycerine in the back.
Is this Sikorsky unmanned?
Modern electric motors are about twice as efficient as IC engines, but an order of magnitude improvement in battery energy density will still only get you half as far. Fuel-cells might be a better option, but they keep on stubbornly refusing to live up to their potential. Pun intended
