Why can't I equip this module?
It's probably unidentified (the tooltip says so).
You'll need
ORE- Read the module's tooltip. Anything above Normal rarity can drop unidentified: its modifiers, ports and rating are hidden and it can't be fitted.
- Identify it by right-clicking with enough ORE in your stash; the tooltip shows the cost. It costs 10% of the item's rating, at least 1 ORE.
- Fit it while tethered to a refit terminal. In a hub your ship tethers to the pad automatically.
Still won't fit? A battery, subsystem or propulsion module must cover a matching hardpoint, and a hull can't carry more battery modules than it has battery hardpoints.