I recently bought a sp4 and i have it powered by a hifonics colossus, im getting a 350 amp alternator and just wondering if i need a bigger battery? Whats the point of a bigger battery cause once the car's started the alternator takes over for the electrical system right? The 350 amp alternator should be more than enough to give the amp all that it needs right?

The point of the battery is if you were playing music with the car idling or with the car off. Even if you don't do either of those things, I would still have a good size battery just in case. Say your alt for whatever reason stops working, or doesn't work as well as it should. Now your voltage is going to bomb hard because you don't have hardly any battery reserve to hold it up.

Batteries and alts go hand in hand. You can't really just have one or the other, they both play an important part.

Once your car is running, the electrical system does not run off of the alternator. It runs off the battery. The only difference is that now that the car is on, the Alternator recharges the battery. Alternators are just mobile battery chargers, that's it.

If you just have your normal starter battery, you're going to need an extra larger one. You're going to be discharging and charging that battery so rapidly that it's life will be decreased substantially.

Once your car is running, the electrical system does not run off of the alternator. It runs off the battery. The only difference is that now that the car is on, the Alternator recharges the battery. Alternators are just mobile battery chargers, that's it.

If you just have your normal starter battery, you're going to need an extra larger one. You're going to be discharging and charging that battery so rapidly that it's life will be decreased substantially.

No, that is incorrect.

The point of your battery is it for it to be there to start your car, it is reserve capacity.

Once you have started your car you can remove the battery and it will continue to run because the alternator is running the electrical system because it produces electricity by spinning and creating a field. Do not attempt to drive the car because the alternator will full field and charge at 20+ volts because it will see that there is no battery and it will see it as "dead".

To the OP - Yes, you need to add a bigger (preferably AGM or Dry cell) style battery to increase your reserve capacity for your electrical system.

The point of a larger battery is burst reserve.

Music played is dynamic and VERY fast.

The alternator has a time delay in seeing requests to supply more current.

Today's batteries do not.

Those quick bass notes will pull from the battery but then be immediately taken over by the alternator... at least as long as the bass note doesn't shift it's amplitude or frequency!

The smaller the battery in this environment, the deeper the discharge. The deeper the discharge, the less life this battery will have before it dies.

Also, the smaller the battery, the lower your voltage will drop on sudden bass notes too.

And to reply above, the reason the battery is not in full control when vehicle is on is simple...

WHOEVER has the HIGHEST voltage in the vehicle with the ability to supply a LOAD WILL support the demand of power.

Once you have started your car you can remove the battery and it will continue to run because the alternator is running the electrical system because it produces electricity by spinning and creating a field. Do not attempt to drive the car because the alternator will full field and charge at 20+ volts because it will see that there is no battery and it will see it as "dead".

Thank you for the correction.