Im going to save matt a lot of time and say that is pointless and will actually hurt your electrical system instead of help it. especially with a H/O alt. save the time and money. big three and H/O good idea second battery bad. unless you wanted to sit with your car off listening to music for say six hours then you could justify it but if your doing that why not get a little battery powered stereo. just saying. if you would like me to explain why I will but its easier to just say trust me