My alternator is overcharging my batteries intermittently. I could measure a peak of 16V on short durationss but most of the time it's charging OK at around 14.5V. I'm not sure if the alternator is already faulty but I have doubts. Could a bad engine grounding cause this unstable voltage? I can't seem to locate the grounding cable from the engine to the chassis although the negative terminal of the battery is well grounded to the chassis. Could this be the problem?