Q: how can i fix the charging issues from the alternator to battery

my jeep was dieing on the road while driving, because the volts were falling to 0. i had the alternator{6m old} and battery tested (2 weeks old) to make sure they weren't bad. i proceeded to install a external voltage regulator and unhook the wiring system from the alternator to see if i could charge the battery that way, with no success. as it sits there are no internal wires hooked up to the alternator. i wired up the external to the alternator and battery with no charge. now i have to say with the external wires hooked up to the battery it showed it was charging twice for only 20 min each time, but then droped back down to 0. the volt gage was jumping from 6. to 14. volts on the battery never settling on one number during this time. im out of ideas and could use help

My car has 180000 miles.
My car has an automatic transmission.