I have a 04 RX8 that the other day we were gone camping for about 5 days. When I got in the car was dead, so I thought ok its the batery. I bought a new battery, put it on and it started right up. But when I came to a stop light or stop sign it seems that the RPM'S go down real low almost to where it would die. My wife drove the car today and she said it died on her twice. Could this be a alternator issue now?