I am wondering if i should run a seperate battery in my car for subs before i install them. i have a big fuel pump that uses alot of voltage and the procharger which draws alot of power too. i have alpine deck one the newest one's 50x4 amp set up, also have a 75 watt alpine deck for the speakers. the sub system that i am going to run is 2 10" memphis m class subs with a single 500watt amp. the car has a 145 amp alternator in it. the car already has a bit of trouble running the 75 watt amp some times. so would it be a good idea to run a seperate battery or what?

 

instead of a 2nd battery you are probably wanting to look into a higher output alternator... depending on current draw all of your equipment has you need an alt that can easily run everything .....

it dosnt matter how much storage you have (battorys) if you dont have enough amperage to refill it (big enough alt)

 

then seeing how your making enough amperage you mind as well store that extra amperage by running another battery. Idk what kind of battery you have but I have a Optima Red Top which are great for starting but not systems and then i have a Kinetik Power Cell in the back for my system. The power cell is just the car audio worlds deep cycle battery. Idk how you cant power your amp tho. I have two 500 watt at 2 ohm amps pushing my subs and it doesnt dim or even move the amp gauge at any load. I can have lights/ac or heat/radio bumping a hardcore bass song/ and interior lights on at an idle and it still wont dim the lights or move the amperage gauge. Before the power cell...haha that was another story...my lights would dim to almost nothing and all i would have on is headlights and radio. Here is a pic of the power cell in the lock box...

 

It seems very hard to believe that the vehicle is having a hard time keeping up if your current alt and battery are in good shape. Your fuel pump may draw some amperage (not voltage), but no where near what a good size class-a/b amp would. Have you upgraded any of the underhood power wiring yet? That would be your first upgrade. Is the alternator an aftermarket upgrade? If so, that may be why you're having a problem, especially if its at lower RPMs.

It sounds like you've got a weak link in the electrical system and adding a battery is only going to cover it up instead of correcting the problem.