Q: Ok so i just got a use but like new alternator on my 2011 chevy cruze and a brand new battery

The voltage output of the alternator should be tested at the battery terminals while the engine is running. You should read output of 13.8 volts on up to maybe 14.4 volts but the value (and range, which is dependent on engine RPM) will depend on your Factory Service Manual Specification which the Mechanic will have on hand. You also have to look at the output while running various circuits. It could be that there is a short in one of those circuits which causes battery voltage to drop below the threshold at which the warning light will set. My initial suspicion would be the alternator is simply out of spec. What I would recommend is having a certified professional from YourMechanic perform an inspection of your battery and charging system which will identify the root cause of this issue you are having. Once the cause is understood, he or she will explain the repair strategy and cost. Please let us know how we can assist you further or if you have additional questions.