I've got a '99 Ultra Groundpounder with an S&S 113" motor. The battery has a charge of 12 or 13volts when cold, when I try to start it, the battery voltage goes to around 4 volts and obviously doesn't crank the motor. The battery is only 2 weeks old, not on a tender. If I jump it from my truck, it starts immediately. If I turn it off and try again by itself, it won't start. This is a curse on this damn bike, this is my 6th battery in 3 years. Any ideas?