macbook pro 13 (2009) battery not charging.. (battery is not the problem)

ok so I looked around and didn't find the info I was looking for; my apologies if there are other threads about this. I'm at a loss as to what to do about my macbook pro; the battery will not charge.. sometimes the indicator has an X through it and sometimes it just says (not charging). I HAVE confirmed the battery is not the problem, as I've replaced it with a battery that I know to be fine. The computer works fine as long as its plugged in, but the second i unplug the ac adapter the computer cuts off.

I've tried all the tricks like pressing "shift-control-option and power," as well as the command-option p and r.. (even the o, and f one although it had no effect at all). At this point I'm assuming it's a motherboard issue. I've read that there's a logic chip or something like that which the battery connects to, and that can be replaced. I guess my only option is to take it to either a certified mac service center or an apple store?

I guess I'm just curious if anyone has ever seen this before and if so how was it resolved? is it something that will be astronomically expensive? Any info anyone could provide would be greatly appreciated. Thanks in advance and again sorry if this has been adressed already..