G. Kashkanun Anderson
SOC-13
The LBB:5 text does not say you cannot jump without a full complement of Jump Fuel; it says you need the Jump Capacitors charged and sufficient fuel in order to make the jump.We also know that anti-matter Jump ships without giant LH2 fuel tanks are possible at higher TLs. So it is not a physical impossibility to jump without jump fuel. The designers just did not want us to do it.
The difference is this: It is established in CT (I think by Marc Miller's JTAS #24 article at least, if not by LBB:5) that there is a hull-length Jump Grid that needs to be maintained in good working order, or else making a jump is de facto extremely difficult, if not impossible. Whereas the Jump Drive does its energy-intensive work only during the actual space-fabric ripping part of the jump, the Jump Grid needs to be up and powered for the entire 168+ hours of the jump, because Things Which Old Spacers Never Discuss happen to those who come in contact with the eldritch physics of Jump Space. And I doubt you can run that grid on battery juice, because keeping an entirely alien set of cosmological laws at bay ain't hay, and it ain't cheap.
There is nothing in the literature, as far as I know, about which system maintains the Jump Grid. My money's on the Jump Drive itself, since jump-capable ships don't appear to have any extra Power Plant requirements over non-jump boats. Marc Miller's article also mentions that 'some' of the Jump Fuel is spent on 'carrying off fusion by-products, and in cooling the system' during the jump proper. Not all the fuel for the Jump Drive, mind you, but some -- an unquantified, yet 'sufficient', amount -- is necessary.
There are also other non-optional systems of the ship that need power during the entire jump, like life support (of course), various electronics and grav plating; I don't know about you, but I get pretty cranky when I have to drink my coffee a week old, cold, and in a zero-gee vacuum. It is possible to run some of those systems on batteries, and you probably can if you find yourself forced to make an emergency capacitor jump out of a hot situation, but it is likely not recommended. Much better to have 'sufficient fuel' for the trip -- at least enough for regular power plant operations, and definitely enough to keep the Jump Grid up and running.