I think shield powering is too draining to sustain during flight. I think this could be remedied by a few things:
1) have a block that automates turning on and off shields when in combat, similar to how repairs work, but maybe lasting a little longer after a battle. This could also coordinate with the Sensor Array to detect when an enemy gets too close to turn on the shields.
2)In Star Wars/Trek you always see the Captain of the ship say to the crew set the shields to full (or something along those lines) and the entire ship is shielded. Also its a pain to go through and turn off every last shield in a ship, so I think if you select one shield gen, and then press let's say Shift+P and all of the shield gens turn on. This could also be used for every other block that you can turn on and off, and with firing at will.
3) Most simply, shield gens could just use less power. However, I think this would be the worst option, since that would make shields too OP.