Your battery is kaput. Just because you generate enough juice to run (while it's running) doesn't mean there is a surplus available for charging - might be, but not necessarily. Do the earth wiring mod from your R/R if you haven't already.

Cheers, Richard
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09 America, Staintune Pipes, K&N, Breathe, Hagon Nitros, AI & O2 removed, tune 20184 (modified), MTX-L a/f gauge