I bought a revenant and tried equipping a light power cell on it and it and it turns red when I equip it. I then tried to equip the ec-101 with a light power cell and it does the same thing, what am I missing?

Its just the UI you are probably on an item select that wont fit into that slot

You've likely selected one of the weapon slots instead of selecting the power cell slot when trying to equip it.

I found the problem. It wasnt my power cell at all, my grouping (under ship configuration) was all jacked up. I appreciate the help, thank yall.