Why might a car not start after installing a new battery?

Answer

Without buying expensive test equipment, you can test it by replacing the questionable part with a known good part.

did you have the new batt.tested where you bought it?you can get a bad batt.off the shelf i know. starter draging.just went though this myself

Even though its a new battery, it may be the alternator!! the easiest way to check it is to get it started when running, take the negative cable or black cable off of your battery if it stays running your alternator is fine if it dies the alternator is bad!! the alternator helps keep the battery charged and going!!