Voltage is low after new battery altnator keep going

If you have a new battery and a new alternator. The first thing to do is make sure you have a full charge on the battery. Just because the battery is new, does not mean it is fully charged after sitting in the store, maybe for months. Assuming the alternator output is correct, it may not be able to charge the battery AND supply your car with power. This is true especially if you only drive a short distance to work. If you do not own or can borrow a charger, take the car out for a longer drive and see if the undercharge condition improves.