Q: Car wont start, new battery alternator is good only turns on with battery charger.

It is common for a bad connection in the starting system to cause problems such as this. When you add the battery charger, it give it a little extra boost in voltage. Just enough to overcome the high resistance. The trick is to find the connection that is the culprit. There are a number of tactics you can use to find the source of the problem. If you are tech savy and know how to use a mulit-meter to do a voltage drop test, this is the most accurate method. Most don’t know how to do this properly. So the next technique is to connect that battery charger, disable the ignition system so the car won’t start, and crank the motor until you find a hot connection in the starting circuit. You will be able to feel a significant increase in temperature at the point of the bad connection.

High resistance creates friction and therefore heat.

The next possibility that comes to mind is an overnight draw. A draw is a drain on the battery that happens when the car is off. Everything will work normally once the car is started, but it won’t crank in the morning. You will know if this is a possibility by whether or not the car starts after you have been driving it for awhile and you turn it off to go into a store or something. A draw won’t drain the battery fast enough for it not to start after a short stop, but if there is high resistance, it will be made worse after driving because it will already be hot from motor.

I recommend getting your car looked at by a certified technician, such as one from YourMechanic, who can diagnose your starting issue and help you fix it accordingly.

Good luck!