My neighbor has a 1985 Corvette. Every week or so he would pop over and pick my brain trying to get his vette to start. Every single time I told him to check his battery I got the dreaded "battery is brand new" remark. I would give him the same response as Melsg5 said to you, unless you load tested the battery I don't care if it's new or 10 years old it can still be the culprit. He installed the new battery in the spring, moved it once into his storage tent and it never started again.
Long story short, he finally just said the magic words "I'll pay you to come fix my Vette". Normally I have zero issues helping people for no financial gains but this guy has multiple lake front properties he just sold and was bragging about how many Millions he made. He also has 6 cars and was left a fortune by his parents. I don't judge people but also don't like being taken advantage of. If he wants to fix his own car I'll help by giving him knowledge, what he does with that is up to him. If he was a little old lady on a fixed income I wouldn't hesitate to even give her a battery at no charge and install it for her. I just don't want people thinking I'm a money hungry person. Anyway I went over there and the battery had ZERO energy. I mean it couldn't even supply 1mA of current and all the cells were completely dead. Further testing showed he had a parasitic drain of 8 amps on a 15 amp circuit so it never blew a fuse but it would kill a battery overnight. He doesn't use the car much so it sat there on an 8 amp load for god knows how long before he needed to move it again.
Moral of the story is a new battery can be dead. You can also have a battery showing over 12v but cannot deliver enough current to start the motor since it's internal impedance has risen too high from Sulfated plates. This is why a load test is the only certain way to tell if the battery is in good health.
You don't need a load tester. The starter motor is a real world load. Place volt meter across battery, if you have over 12v start the car while watching the volt meter, if the voltage droops down below 10v the battery is junk. If when you turn the key the battery stays at 12v or higher than there is something else wrong and the battery is not the problem.
