I just came in from the garage. The battery showed 12.9 v after it was charged.I started it up and it droped to 12.0v at the battery.As i reved it up voltage would go up. As soon as i would let off the gas voltage would drop to 12.0 and into the 11`s. I thought it was the alt or voltage regulator but because of the voltage increase when reving is it a bad battery ?? It does have a 4 prong ballast resistor. The battery is a optima red top about 3 years old. What other should i do?