Managing powerIn Elite: Dangerous we can manage our power-systems with more detail. If you open up your ship page, then move to the tab marked modules which should look similar to this;
What does this mean? well on this tab we can prioritise power to our sub-systems (1 being highest, 5 lowest). So when we dont have enough power for everything, we can tell our ship where to put the power first. By default, everything is set to 1 which means every subsystem has an equal chance of power. This is fine most of the time until there isnt enough energy for everything (we dont want some systems running out of power). ie. we dont want our shields to go out when deploying your lasers for example (shields are more important in a fight).
So I would recommend leaving all important subsystems at 1 (like shields, power distribution etc.), weapons at 2, and less important systems (drive, sensors, life-support) to either 3, 4 or 5 (such as the cargo-hatch). However you may wish to change some weapons / subsystem to different levels depending on your situation or setup (ie. you may find your weapons are more important, or less). So adjust the levels to your own requirement. I would suggest setting your Cargo Hatch to 5. As long there is some power for them, they should remain working.
You may also notice each subsystem has an assigned type, these correspond to our subsystem power allocation. So we can prioritise each type of subsystem, then each subsystem in it. ie. SYS subsystems could have 1 unit of energy (set on the HUD), of-which shields use it first, then life-support.
This may sounds rather complex, but it allows you to send your power to where you need/want in certain situtions.