if you have way more or less than 13.8-14v at the battery during idle, your rectifier (AND potentially, stator) are bad. After that test, you want to unhook the stator plug to the rectifier, and hold RPM to 4000rpm and you should see something like 60V AC. The Stator produces AC, and the rectifier/regulator converts to DC. I literally just did this this weekend at the race track when my rectifier cooked.
You should always also check your stator as they can both go at the same time.