My alternator pretty much died this week. The battery kept draining every night & since it was old I replaced it. Surprise, the next morning it was dead to! When I checked the voltage today while the car was running it was at 13 volts. That seems kinda low to me. Also, by the time I got home, the car wouldn't even start. Am I wrong in thinking that the alternator is bad? What would be a good replacment alternator? Thanks....