I'm thinking your battery is pretty much toast and you need a new one. I've always been told to never start a car with the motorcycle battery hooked up to the cars battery as the extra energy spike from the car's alternator can be enough to destroy the battery.
Until you hook up a volt meter to the battery to test the voltage, there is no way to know for sure. However, since you said you've had the charger hooked up for several day's I would guess that you have a damaged/shorted cell in the battery and it's simply done with.
......I'd rather wake up in the middle of nowhere then in any city on earth.
*2014 VN900 Custom (16,200 miles and counting)