Check engine lights are not a 'gimmick' its not some big dealership conspiracy, it means there is an emissions related problem. Could be a missfire, evap leak (gas cap, which sounds like you bought one), air fule ratio issue etc. Like others have said, go to schucks, have them pull the code for free, and google the code(s) or post it up here and go from there. Disconnecting your battery will not make a problem go away, it does 'reset'your ecu, but if you truly have a problem your cel will come back on, let us know what code you have....