i guess it depends on what you mean by "different charge levels", what about taking the "dead" pair of cells out of the G2, lets say, and putting *both* of those cells in the X5, i'd imagine that *should* be safe, as they were both used in the same light initially, they both should be at the same discharge level....
now, taking one cell from the G2, and one from the X0, *that* would be dangerous....
am i on the right track here?
how about taking a piece of adhesive (or electrical) tape, and tape the "dead" batteries together (side by side) so you know which ones have been paired correctly if you need to store them before using them in the battery sucker?