Currently the only "advantage" of big batteries or fuel tank is that it takes less time than to place, however the smaller parts make it easier to squeeze them in. For fuel tanks the bigger ones also deal disproportionatly more damage (50, 100, 500) on explosion. There should be an upside to using a 2x2 block instead of 4 1x1 or 2 1x2 blocks. This would then also properly scale with the increased danger of a bigger fuel tank.
Since we already have the supercapacitor and booster tank it would make the most sense in my eyes to boost the energy/fuel regeneration of the bigger blocks and slightly reduce the regeneration of the 1x1 blocks. Maybe 5/8 for 1x1 to 3/5, 1x2 stays the same and 2x2 gets buffed to 25/40.
Another interesting thing would be connection bonuses. For example connecting a shield or weapon on a battery could reduce their energy requirements by 10% and connecting thrusters to fuel tanks could reduce fuel requirements by 10%. This bonus could scale with blocksize.
