8.5V! sure sounds like a goner to me...not sure but I vaguely remember reading something like if the battery reads <10v, it's done. In any event, i keep mine on a Tender, so not exactly comparable, but I start out at 12.8 or so, put key on with no headlight and it moves maybe .1, put headlight on and it drops to 12.2 and stayed there a good minute anyway. So yeah, I think yours has waved sayonara.
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-Jim
'93 MC21