2003 C240 87k miles

While swapping a battery I read you can use obdii port to hook a power source so as to keep computers supplied. Hooked up and obdii cable with alligator clips at the other end. Soon as I plug it in theres a beep beep sound. Well I had a 12v car battery and used that. While removing the old battery the +ve did touch the body and there was a slight spark. Completed the install but now my obdii port and cigarette lighter are both not working. I looked at all the fuses under the hood (driver side) and on the driver side dash end but they are all ok. What am I missing? Also is it ok to hook a 12v car battery into obdii port or should I hve used a 9v battery instead?