mr.onzedge- while you were on your painful biztrip to hawaii
was your car hooked up to a battery manager or your kids drive your Z around while you were out?
i ask because there might be some link (not verified) of cars with lower battery charge having this issue more than others.
especially for those in very hot or very cold climates cca can vary greatly...and 3yrs is about when batteries start to show wear if not on battery manager.