I have a 2005 LS2 with just exhaust mods. The car has been sitting for a few weeks and I went to start it and it started slow, however it did start. The car ran for about 2 to 3 minutes in the garage and it cut off. The computer flashed a message when it cut off and said Safety Mode Engaged / Reduced performance. I cut the key off and tried to start it again and it wouldn't even try to start. I disconnected the battery and reset the computer and it started up and ran for 2 to 3 minutes and cut off again. I took the battery and had it checked and it only had 22% charge on it, however after they charged it they said the battery was good. I'm unsure what it could be, could someone help me?