Car won't start after replacing the battery. Checked alternator for lossness. on 2000 Volvo S70

Drained the battery overnight by leaving the headlights on. Replaced the battery, checked the alternator for loss wires since the car now won't hold a charge.

Asked by for the 2000 Volvo S70
check charging system should be between 13.8 and 14.2 volts