I have a 01 jetta, Does the altenator charge all the time? I check the voltage when the car is running and sometimes it shows only 12 volts, i can turn the car off and re start it and the voltage will go to 13.5 volts. When it reads (whatever volts is in battery) 12 volts and car is running, i put load tester on it and flip switch and the altenator kicks right in and will pull the engine down from being under such load. I took altenator to shop and mechanic says it is okay. I guess my question is this normal, or does it supposed to charge all the the time, or does it just charge when voltage gets low (maybe to conserve horsepower for economy) any info will be helpful.