Wel, Its time for another topic in this section...... The addition of a second battery to your adio system. First, WHY would you need to install a second battery????? Welp, pretty simple really, It gives your amp the added capacity to produce its short term peaks, and allows for longer play times at reduced alternator output levels. (and if you do it right, you can jump start your car without ever leaving the cabin, or having another car, ask me later!!! ) Lets start at the fornt of the car. You have your existing electrical sytem already upgraded and performing to its max by upgrading the big 3?/? Right??? Do this first before you go any further here!!!!! Now, what does it take to do a second battery? Just a few things, most of you are familiar with, and one you may not be. First find a location in the back of your vehicle to mount the battery. I suggest an enclosed type marine battery holder, they can be had for around 15 bucks and they contain the battery and prevent any spils into the interior. Find a location that allow for relatively easy access and servicability. Once you have your spot staked out, lets move on to the wire. the wire for this battery to maintain a charge does NOT have to be HUGE....4 AWG is more than adequate and will transfer all the power that is reguired of your amp and keeping the battery charged.... The Wire itself, that runs from the front of your car to the rear will need TWO fuses, each within 18 inches of each battery. One at the front, and one at the rear battery. These fuses prevent the wire from gong into thermal overload (BURN) if it ever get shorted out!!!!!! Use ANL type fuses, NOTHING ELSE!!!! The ANL type fuses handle the curent properly and are 100% reliable. Any other type of fuse holder is second rate at best.....PERIOD. 100 amp fuses will do just fine in most applications. but no bigger than 200 amp.... Now, the next thing on the list is VERY important. A relay. A BIG relay. This is critical in allowing 2 batteries to co-exist in the same car without literally killing each other. If you put in 2 different batterys, of different size, CCA,age,reserve power, health, etc, you WILL kill them!!!!!!!!! BOTH of them!! What you want to do is allow both batteries to work in unison with each other to power up your amps, and still get a charge from the alternator, AND not let them die from setting hooked up together when NO charge current is available (when you shut the car off an let it set for 2 weeks when your off on a vacation nailing your best freinds sister when he is drunk passed out on the floor)........ the KEY to allowing both batteies to live with one another is to install a RELAY. The relay serves a simple purpose in life. It allows both batts. to be connected in parallel when the car is running and the aternator is charging, and allows the amps to pull current from both batteries. It also DISCONNECTS both batteies when the car is off and the alternator is NOT charging, thereby preventing the batteris form killing each other. With this method, you can use ANY 2 batteries......Its simple, and it WORKS The realy i am reffering to is a 200 amp unit. http://www.sonicelectronix.com/item_5287.html This one has been around for years and is fairly reliable ( seen a few failures) The relay can be mounted in front under the hood, or in back , does not matter, it is simply an electro mechanical switch, it dont care where its at. Just BE SURE it is mounted properly and securely, those 2 big terminals on top have ALOT of current to kick out if the thing shorts out and will blow the 2 fuses!!!!! From the front battery go to one side of the relay, from the back battery, go to the other one, simple. Now, one of the smaller terminals needs to go to a good ground, the OTHER small terminal needs to go to a switched power source. A few options on this one. i always hooked it up to a source of ignition voltage that was not LIVE when the car was being started. But was live when the car is running. Radio ignition lead would work fine, Be sure to fuse this lead also..(2 amp fuse) You COULD hook this lead up to a voltage source that is HOT while cranking the engine over, but I DONT reccomend it (hard on the relay). Oh yes, the ground for the secong battery, same rules apply, all paint cleaned off to shiny metal and a BOLT holding it down....NOT a seat bolt, NOT a seat belt bolt, and NOT a factory ground!!!!!!!!!!!!!!! If your gunna do this, do it RIGHT!!!!!!! Now, everything is installed, all hooked up and ready to go. when you turn on the cars iginition you should hear a "click" from the realy. GOOD!!!! when you shut off the car you should hear another "click" from the realy....GOOD!!! iIt is turning off and on as it should! Now start the car and measure battery voltage at EACH battery, they should be near IDENTICAL!!!! IIf not, you have issues!!! You are DONE!!!!!!!!!! You now are able to allow your amps to run off 2 batterys and yet allow neither nattery to kill the other!!!!!! The ONLY way other than this to hook up 2 batterys is to install 2 new batteies, BOTH of the same size and age.......THEN you could not worry about the installation of the realy....If you put in a new fangled yellow top. red tp. blue and green top, or even a carrot top with your existing battery without a relay, then you ae asking for problems.... As always, i open this up to LOGICAL and REASONABLE discussion/questions.... Thanks for listening folks, i am here to help you get the most out of your car audio!!!!!