I worked on a refueling station a few years ago. The purpose was to, instead of hooking up a ship via connector and funneling hydrogen into its tanks, have replaceable, pre-filled "fuel cells" which the station would replace.
The fuel cells I was working with were 2 large grid hydrogen tanks surrounded by some structural blocks to make them look pretty--they kinda looked like a big battery. Their overall size was 5x5x9, IIRC. Actually, technically 4x4x9, since I surrounded them with half-block variants instead of full blocks. But they couldn't fit in a 4x4x9 space, so 5x5x9. The system had 5 bays for storing these cells (with potential for more if I really wanted to). They would fold out of the ceiling to reveal the cells, so that a sort of conveyor structure could pull them out of the bays and take them to the end of the storage room and then up through the ceiling where the landing pad would be for ships getting their cells replaced. The cell the ship already had would then be brought back to the now vacant storage bay for refilling.
It had a program running that would show some key stats on LCDs, and when a certain function was called, the system would find the most full cell (or just the first one it finds at 100% out of the array, if any), take it out of its bay and move it off to the landing pad. And it could do the reverse, bringing a cell back from the landing pad and putting it into the first empty bay it finds. I never got far enough to actually have cells taken off and put onto a ship, though.
The most obvious drawback is that this system was incredibly slow. It took about 50 seconds to a minute for a cell to go from a storage bay to the landing pad, and vise versa. This was the quickest I could make the pistons and rotors go without inducing Clang. If I'd gotten any further, it might have taken another 30-40 seconds to replace a cell on a ship if I had to guess. For 2 large hydrogen tanks, it's far quicker to just transfer the hydrogen through a connector, so I stopped working on it. And that's not even considering the fact that ships would need to be specifically designed so that the replacement process of cells wouldn't need to be different from ship-to-ship. Just too much hassle for no added benefit.
I really loved that concept, though.