the vecs are powered by cool fusion, and thus would never need refueling
needing it would require, in my opinion, a needless sourse of micromangement, plus on a different planet, not only would fossil fuels not exist (it comes from long dead plans) it wouldnt burn in the atmosphere
now ammo on the other hand is a different story, I always thought it was kinda stupid that an rpg lynx could shoot off rocket after rocket, forever without ever needing to refuel
now energy based wes like laser, microwave, and thors hammer, I can understand, but other vecs should have a supply line
mabe it would be invisible drones, that would go from the vec, to the nearest vec fact or garage, and they would periodicly rearm the vecs, this means that the farther away the unit is, the less it gets resupplied, and the drones cant go past enemy units, so that encircling units could starve them of ammo, or at least delay their resupply considably
that would add another layer of realism and stratigy, without adding more micromangement
just an idea