just because a battery is charged does not mean that it actually is. Battery's hold a surface charge, and when you go to start the engine it takes A LOT of power. So the battery goes back to its original dead self. It might be new but I've bought a couple of battery's in my day that where dead. Just go back and use the warranty on the battery, like the life time warranty. I haven't bought a battery ever for my car except one! haha. But thats besides the point. Other things to look for, did you put all the correct wires in the correct spots and tightened down tight enough? You should have a wire on the ignition termanl and two on the B-terminal. They will come lose very easily if not tight enough. The battery cables must be TIGHT. They just can't be half assed. These are some things to long into. Electricity is a b*tch... trust me.