How can I tell if I need a voltage regulator, or if an alternator will do the trick?

My car was running fine, then it just ran out of power,after I changed the battery it worked fine for one trip to work (not back) helpHow can I tell if I need a voltage regulator, or if an alternator will do the trick?Use a voltmeter, measure the voltage on the battery when it's not running, then start it and check the voltage. Should be like 12.5 volts when it's not running, and like 13.75 volts when running. If it doesn't increase while running, you need an alternator.How can I tell if I need a voltage regulator, or if an alternator will do the trick?You can have the people at Checkers test your alternator but you may need to take it off. Some Checkers Auto places have a portable one. However, it does sound like your alternator. So old cars also have wiring issue.How can I tell if I need a voltage regulator, or if an alternator will do the trick?Take it to the service station and they will put a test meter on it and they will be able to tell you what the problem is. I believe Walmart has one or your local service repair station will assist you. It's very easy and only takes a few minutes.How can I tell if I need a voltage regulator, or if an alternator will do the trick?I wouldn't suggest a change in alternators or voltage regulators until you've gone to a professional mechanic. How old is your car? Maybe its the wiring and its grounded which is depleting the battery even if it's brand new. Alternators just need cleaning and maybe that's what it needs for now. Better have everything electrical in the car checked first because if you change and it still doesn't work, you just wasted your money on something that didn't need fixing in the first place. Regards.How can I tell if I need a voltage regulator, or if an alternator will do the trick?Most alternators have the regulator built in these days. Just test it. Either start the vehicle and put a cheap voltmeter on the battery (it should go over 13 volts if it's charging) or pull the alternator and take it to your favorite parts store and ask them to test it for you.