How do you connect a secondary car battery to run your system and other electronics in your vehicle?

I want to hook up another battery in the trunk of my car to run my sound system, the underglow and so forth, and I was wondering how I would do that. I know it has to do something with connecting the power and grounds of both batteries and something to that affect, but I'm not 100% sure. If anyone could walk me through it or point me in the right direction of where I could find it that would be great. Thanks. Also, what kind of battery would be best for this situation. Any help would be greatly appriciated. Thanks.How do you connect a secondary car battery to run your system and other electronics in your vehicle?the only reason to hook up another battery in a car is if you want to frequently use alot of power while your cars not running. it will not give you %26quot;more power%26quot; it will just allow you to use your electronics longer when the car is off. if that's the case it would be beneficial to get 2 of the same batteries. to hook it up you just need to run a thick power wire (at least 4 gauge) from the positive end of your main battery to the positive end of the battery in your trunk then ground the negative end of that battery to the frame in your trunk. if its more power you want then upgrade your alternator.How do you connect a secondary car battery to run your system and other electronics in your vehicle?Just install another battery, run the positive to the starter post and the negative to the frame. It will still be 12 volts. To do it wrong and get 24 volts, run the new positive to the old battery negative post [remove the old ground cable] and the new negative to the frame.How do you connect a secondary car battery to run your system and other electronics in your vehicle?go to electronic store or garage where they install devices.