Rebel and Scum only. Modification.
During the End phase, you may receive 1 ion token to recover 1 shield (up to your shield value). You can equip this upgrade only if your shield value is "1".
A ship can only pay the cost to use this ability (receiving one ion token) if it can recover a shield. Therefore this ability cannot be used if the ship has a number of shield tokens equal to its shield value. (X-Wing FAQ, Version 4.4.0, Updated 10/25/2017)
At this time, five ships can equip this card: