Dead battery. Replaced with new. Now won't start

[jagarundi]

Hoping someone can help. Had a dead battery in the X5 over the summer. Got a charge and was able to start. A few weeks later battery died and car sat in the driveway for a couple weeks. Charged the battery but car wouldn't start. Used the spare key and it fired up right away. Fast forward another couple weeks. Battery died and I bought a NEW battery. Took out the old and put in the new. Now spare key doesn't start the car. Bought a battery charger and charged the battery overnight so that it's fully charged. No crank, no sound, no start. Really frustrating as it has now been sitting in my driveway since the summer. Can ANYONE point me in the right direction so that I can get this delicate genius to start?