charging help please
 

i have a 97 cherokee with the 4 liter. sometimes when i drive it its fine and the battery Gauge in my dash is right at 14 volts. other times its half way between 9 and 14 volts and today it was stuck on 9 volts and the check gauge light was on. my jeep ran just fine and my lights didnt dim. i took it to the local auto store and they said my battery was low on charge and my alternator was bad. i have an optima battery that was load tested around a month ago and it tested good. my volt meter read about the 11.8 volts at the alternator wire and the same at the battery when my gauge was at 9 volts. about two weeks ago i made some aught gauge battery cables out of welding wire and brass terminals but i havent gotten around to the alternator wire. my question is do you guys think its a bad wire or a bad alternator. and when an alternator goes bad is it usually this intermittent. thanks for the help.