Don't assume that NEW is OK, both alternators and batteries are defective when out-of-the-box.
Step one for a good tech is to ignore the word NEW and test the system.
A charge system should be putting around 14.6 volts out, and into a battery.
A battery at 12.6 volts is considered OK, but may not be.
If the car starts after sitting a few minutes, but doesn't after it sits "overnight", something in the car is draining it, like a fuel leak empties your gas tank.
There are systems in a modern car that are draining your battery, but "go to sleep" in a short time. If they are defective, it's like an invisible dome light left on, or worse, leaving your headlights on...
Don't assume the parts you replaced are working until someone checks an amperage draw on your battery. Modern cars are a pain, but sometimes throwing parts at them doesn't solve a problem; get someone to check it...