I am having charging issues on my 2004 Elantra. I have had the alternator checked at two different NAPA stores and have replaced the battery. I checked the voltage at the battery this morning with the car running and got a reading of 14.4 volts for about 30 seconds then the motor idle changed and the voltage dropped to 12.0 volts and does not change when I step on the gas to bring idle up to 2000rpm. Any suggestions out there??