The length of time it takes for an engaged interior dome light to drain an auto battery depends on how strong the battery is to begin with, according to Cars Direct. A strong battery is likely to die if the dome light is left on overnight.
However, a weak battery is likely to drain completely within a few hours, according to Cars Direct. Other functions that drain the battery if left on include the car radio, headlights and trunk light. Check the water levels in a car battery to determine whether or not the battery is ready to be replaced.