MacBook Pro 17" 2009 won't works with only AC adapater connected.

My macbook pro A1297 mid2009 appeared to work fine. However, when the battery runs out of power it simply shut down and doesn't come back working until the battery has enough power to turn it on. Then I removed the logic board and observed that when battery is not connected the logic board simply doesn't power on at all. I saw something about the capacitor C7771 and I measured the voltage on it and it's in agreement with the scheme. Does anybody has any idea what could be the issue or anybody has experienced something like this?

Thanks for any response.