Tried search didn't come up with anything....
Are they all the same or are they different?
Can I use fuel from my warship to refuel dropship?
All fusion-powered aerospace vehicles (aerospace fighters, small craft, DropShips, JumpShips, space stations, WarShips) use the same fuel: hydrogen. See p. 42, 124, and especially p. 140-141 ("Fuel") in Strategic Operations. Tech Manual also makes some mention of hydrogen-as-fuel in passing.
Because it seem a lot more weight efficient to store it as fuel for the warship than it does to store it as liquid cargo.
Liquid cargo reflects generic, flexible liquid storage tanks often installed in any standard cargo space, while fuel tanks are optimized, feed-the-engines only things. Liquid cargo, as described in p. 42 SO's example, may be installed in a bay that previously held any other cargo, so there's an understandable loss in weight efficiency. Meanwhile, a WarShip's standard fuel tanks will never be able to hold ammo or food, and if you find either in there something's gone horribly wrong.
I'm not saying it's impossible - I used to work with a US Navy submariner who shared a story about how his sub had to put in for emergency repairs because of an untraceable rattling noise. It turned out to be a large aluminum ladder in a ballast tank that shipyard workers had left in there. So weird things can end up in weird places in ships, it's just the fuel tanks will never have cranes, tie-downs, overhead rails, and other freight-moving provisions you'd find in a cargo bay.
