I've just had a look at my FE2 and an E series lens, basically it should come off.
Now this isn't the voice of experience here, as to my knowledge I have never put a lens of the wrong way up, close, but never quite all the way on.
The lens should come off by turning clockwise.
When you do turn the lens ensure that you have a finger on the black button which is surounded by a chrome ring. This button is at the 3 O'clock position as you look down on the camera with the camera on its back.
By holding this button in you are depressing a small pop up rod which sits in a groove in the lens mount when the lens is on correctly. Without this button pressed you may have some un-wished for aggravation and do more damage.
If your aperture scale is approximately bottom right, then you will have to get it to move a bit more so it is just past 6 O'clock, heading slightly towards 7 O'clock, then it should be able to come off.
I've sort of deduced this by looking at the flanges on my camera and a lens in roughly the position you mentioned. Not scientific, but a pure guestimation.
As for batteries, my experience with the single lithium battery is that they are fine, but when they die they die within a few frames.
The more conventional two battery set-up is more flexible as those batteries will die, you wait a bit and you can shoot again and so forth, you replace the batteries at this stage but usually can still shoot.
Mick.