What is wrong if your car keeps going dead but will start with a boost if the battery is new?

Is it cranking or not cranking? It could be spark plugs that are getting old or spark plug wire problem . Your battery goes down because you try to start the engine to many time. is this a new car with electric anti corosion system this system will drain your battery. the problem is the charging system The alternator may need to be replaced. (A local mechanic or parts shop may sell you a rebuilt one and give you some money back for the old one.) It may just be that the alternator belt needs to be tightened. If you're able to turn the wheel (belt drive) on the outside of the alternator with your own hand (while the car is not running, of course), then the belt is too loose. If you have a crowbar and a wrench and a little bit of muscle, you can tighten the belt yourself.