First check the battery cables for corrosion and make sure the connections are clean and tight. Also check your battery, charge it and check the voltage across the battery terminals under a load, while cranking the voltage need to remain above 10.5 volts.
If that checks out and since you have already replaced the voltage regulator/rectifier most likely it's the stator, check the charging voltage across the battery while running at a fast idle, around 4000 rpm it should be 14-14.5 volts.
Lou
