Relief Charge

Background: Four-room operating room outpatient surgery center that is a part of a large hospital. All OR staff work M-F approx 7-3:30. There is one primary charge nurse (FTE is 0.9) who has the official title and has the charge differential worked into her base rate so she always gets charge pay no matter if she is charge or not. The relief charge is only paid when assigned as charge. So when the permanent charge is assigned in a room as a staff nurse they are still getting charge pay, while the relief charge does not have charge pay when assigned as staff nurse. Relief charge is expected to perform all the same duties as the permanent charge nurse. Currently the split is approx 40/60 relief/permanent. Next month the relief charge will be in charge more than the permanent charge. (as a side note, I have been relief charge for over a year and JUST found out about the other charge nurse always being paid the differential) I want to confront my manager about this. Also, this is a non-union hospital.

What are your thoughts/experiences about this? How often should a true relief charge be assigned as charge?

I feel I know the answer, how should I approach my manager regarding this issue?