Since I needed a scarce resource in my story that eventually leads to war over New Bethlehem, I added the mineral atreidite, which functions like a hyperbattery, a type of battery that can release an enormous amount of energy in milliseconds, which is required to power jumps using a stardrive. The quantity of energy and the speed with which it needs to be released rules out simply using a vessel's powertron directly to power a stardrive. The atreidite gets energized from the powertron over a period of many minutes to hours. This has the advantage that military fleets can't simply jump as far as they want in zero time using just a powertron. They usually need multiple jumps, which eventually drains the atreidite's charge, requiring time to recharge. And atreidite can only be recharged so often, which requires the Republic and Imperium to constantly search for more.
Thing is, I had intended to use two kinds of power generators in my ships and flying vehicles. I figured huge ships should have a different power generator than starfighters and Leonardo's taxi, which use fusion. For one thing, the big ships are supposed to implode-explode when a powertron is ruptured in battle. I had therefore envisioned powertrons to be big enough to power warships and big enough to make them an important target in warship-on-warship fighting. The power source in small vehicles can't be that dangerous since the cab gets damaged a lot in Leonardo's chapter, both from enemy fire and his crazy driving. Remember suicidio mode? 
There are other examples besides the taxi.
A further wrinkle is that interstellar drones have stardrives, meaning they need something powerful enough to charge their atreidite. If I were to say that a fusion generator could charge atreidite, then all spaceships could presumably be fitted with a stardrive since all ships have either a fusion generator or a powertron. I don't want that, though, since I definitely need ships that don't have a stardrive and, therefore, can't jump.
This is making my head spin. One possibility is that anything interstellar has to have a powertron, anything else can use fusion. But if powertrons are small enough to be used by drones, then what prevents warships from using a similary small powertron to power their own stardrives? And the smaller it is, the easier it is to bury deep inside a warship, as far away as possible from the surface of a ship, where it might rupture from enemy fire. Obviously, I don't want to bury it deep within ships since most of my warship battles rely on the powertron to be breachable (or to at least serve as a target).
Another option is to use fusion OR a powertron to charge a stardrive, but if you want to do interstellar jumps with large ships, then you need bigger stardrives than are needed by interstellar drones. The bigger the stardrive, the more atreidite it needs, and the more power it takes to charge the atreidite. So fusion to charge small stardrives and powertron to charge big ones. Obviously big ships also need much more power just to operate.
And, in order to explain why all spaceships don't have stardrives is that atreidite is scarce. So there are small, intrasystem ships with no stardrives (starfighters, shuttles, etc.) and interstellar ships (ranging from drones up to dreadnoughts) with stardrives powered either by fusion (for the small stuff) or by a powertron (for the big ships).
In case you haven't noticed, that's a lot of complexity, which I hate.
Another approach is to continue use atreidite to store power but incorporate the atreidite directly into the vessel's power generation system, rather than just using it inside the stardrive. So, at all times, ships that need a lot of power very quickly, regardless of the purpose (stardrives, heavy cannons, shields, etc.), store some of their power in their atreidite batteries, using them as a reserve power source for when there is an excess demand for power. Non-interstellar ships still won't have atreidite because it's scarce, so they have no reserve power source to handle spikes in power needs such as required to power a stardrive. They simply have to make do with whatever their power generator can put out, and they may have to divert power from one system to another at times (e.g., from weapons to shields, etc.).
I'm going to try using the latter approach. Fortunately, most of the details are within one Galactipedia article. I just have to look at the battles again to be sure nothing breaks.
Wee. What fun. Not.
