Ah, hell, here's the whole process for you. But I want a

ing friend voucher for this.
There is a room past the place where you got the missiles for the ship, behind that orange door, where there are three statues, each activated differently. Activate the one up top (the ice missile one) to freeze the gel waterfall. Go up past the waterfall, and go through the morph ball areas. You'll end up back in the "hidden" room where you will shoot open a new platform that lets you reach the orange-door on the top. That will lead to the statue's head. Have the ship pick it up.
Go back to the room with the three statues, activate the "heat" statue. That leads to a room with two objects that can be destroyed by a "heavy impact". Look for the statue behind the ship missile expansion, drop the head on it, and it will break both objects open. Go through the passage, and you'll see that underground connection pathway I was talking about. Open it on that end (and grab the energy tank between the wall jump area) and notice that you can't yet reach the other side. Go back to your ship, and fly to the area in the lower left (not the main or fuel gel area, the other one).
Go back to the second pirate turret you destroyed earlier (the one through the "left door", if you will). The federation battery is there. Have the ship pick it up. There is a passage right under that battery. It leads to the other side of the underground pathway. Open that end, and go though the now fully-open path, back to the area where you finished the statue. Head back to the "hidden" place, drop the battery next to the gigantic federation mining tower, and you'll see how to FINALLY get the energy cell.