If it's draining even while disconnected, you probably have a bad battery.
With the headlights on high beam, you're supposed to have 14.7-15.5 VDC at the battery at 5,000 RPM. Even if it's only charging at 14.3 volts, I doubt if that's causing the battery to drain while it's sitting. You probably either have a short or a bad battery. I would begin by fully charging the battery and load testing it. My guess is that you have a bad battery.
Most 4-wheeler problems are caused by a loose nut connecting the handlebars and the seat!!
You only need two tools in life -- WD-40 and duct tape. If it doesn't move and should, use the WD-40. If it shouldn't move and does, use the duct tape.