Ok, I'm a idiot.
I took a rock to the chin fairing a while back and it broke off one of the battery box tabs that hold the chin fairing on. I fixed it by gingerly threading a screw through the tab into the battery box and directly into the bottom of my battery. I thought the battery box was a little thicker than that. loks like it ended up draining one of the cells.
Oh well, I've wanted one of those niffty glass matt tech batteries from WestCo for a while now. Gives me a good reason to get one.
Live and learn.
John