Aeion Gauge

The Aeion Gauge is a feature in Metroid: Samus Returns. While in other games it would likely be part of the Heads-Up Display, in Samus Returns it is displayed on the lower screen of the Nintendo 3DS, with the Map. The gauge is a yellow bar that displays the amount of Aeion energy Samus currently has, which depletes as she expends Aeion. It is also depleted if Samus is hit by the Autoad's energy attack. The gauge is fairly easy to replenish however, as Aeion Orbs are given at an extremely high frequency by killed enemies. The Aeion Gauge is also filled after a Chozo Seal is activated, or Samus steps into a Big Aeion Orb.

Manual
"Aeion energy from this gauge is expended whenever Aeion abilities are used."