MBP 17" says no battery, but a battery is in use?

Hey guys, I have a MacBook Pro 17" Intel Core 2 Duo (Pre-unibody) and i have some trouble with my battery. I am using my MBP without being plugged in and it shows that no battery is available with a 'X' over the battery icon even tough i am using the battery as power! The battery is brand new and still shows the green lights on the power indicator, so i know its not the battery thats causing it. Also, at certain times when its plugged in to the A/C Adapter (while battery is in) and i unplug it from the wall, the computer will shut off! but then i close it, take out the battery, re-insert it, and everything works fine! How can i fix this? Ive also tried the 'Battery Update 1.3' and it says i dont need it. Any ideas? 😕