If you are talking about a direct connection to the battery for a stereo on the pos. side, don't do it... if you are talking about grounding directly to the battery I wouldn't recommend that either as grounds are supposed to be 12" or less. I would put money that the problem is with your ground and not your pos. wire. What exactly are you grounded to right now? Was the CD player installed with a wiring harness, or a chop n' splice method?