I recently had to buy a battery for my girlfriends car, it failed with the cold temperatures lately (battery was also nearly 5 years old). In order to get warranty on the battery i had to go down to the shop to check the charging system in the car. The guy hooked up an analyzer did some tests (starting voltage, battery voltage unloaded, battery voltage loaded,...) and goofed up the first time; when the analyzer asked to load the battery and run the angine at 2000rpm he took a while to find the rear window heater and by the time he had the engine revved up the analyzer sayd he had completed this step. Result was that the analyzer said that there was a problem in the charging system, that alternator voltage was to low when it's loaded. Of coarse there was I said, the car was idling when the analyzer said to run at 2000rpm. The guy was starting to make an appointment to replace the alternator, but I convinced him to take the test over. This time he did it right but then there was another problem, the analyzer said that there is a to high diode ripple. I couldn't help feeling that I was being fooled and refused to leave the car behind to replace the alternator. Now I would like to check the ripple myself, how much ripple can the battery take, quite a lot I presume? Am I right that I can check this with a multimeter set on AC voltage, or should I use a scope? Btw, test results from the analyzer said that voltage unloaded was 13.65V, and loaded 13.20V, those are quite normal values I presume?
PS : Sorry if I blabbed along the whole story, for those who hate long stories, the main question is : what's the maximum ripple a car alternator may produce?