[turbostar]

Richard, as I understand it the alternator should not charge as high as 17.5v, as the main purpose of the voltage regulator is to prevent overcharging. My best guess is that the internal voltage regulator in the alternator is failing. Even a weak battery will result in maybe 15.5v-16v charging. Don't know what kind of test was done on your alternator but sure sounds like you are overcharging your battery and need a replacement alternator. Hope this helps fwiw.