Do I need a upgraded battery

[crownvictoria31]

I have a 2005 crown vic lx sport. Just updated my system. My old set up consisted of four 8" seleniums mids on rear deck with 4 pioneer 3.5" bullet tweeters and one 6" selenium on each front door with a dome pioneer tweeter. Rear mids were ran on a mb quart onxy125.4 and tweeters and front door speakers on a 5 channel mb quart which also gace my 500 watts rms for a jbl subs I had. Sounded pretty nice and clear.

New systrem:

four 10" pwx crescendo wired down to 2ohms per channel on fiberglassed rear deck being pushed by a Lanzer opti700x2

three 3.5" pioneer bullet tweeters on rear deck running off a rockford fosgate prime 600x4D(also running the front door speakers off this amp.

Missing my subs which I still don't know what I'm getting but has to be able to handle 1200 watts rms because the amp is a Rockford fosgate prime 1200x1d

I have a p71 2009 crown vic 200amp alternator installed with a modified external adjustable voltage regulator. Had my mechanic bypass the pcm. I have it charging at a steady 14.5V.

Big 3 done with 2/0 gauge wire. Less then a year old interstate mega tron plus battery group 65 CCA-875/ RC MIN-165/ CA-1095

1/0 gauge wire ran to the back.

Problem I'm having is the following:

At the start up everything seems fine. I am able to pump my beats nice and loud for maybe a good 45 mins to an hour or so. Do have in mind, I still have no bass set up so I'm just running mids and highs right now. Then my voltage starts dropping and going nuts at around 13 to 12 volts and dancing with the beats. My question here to you experts is the following:

Ive been looking at the XS POWER D6500 battery which will fit nice under the hood for a replacement to the interstate. I'm looking at about 3000 watts RMS with subs and everything after I'm done. Will replacing my interstate with a XS POWER D6500 resolve my issue or will I need to add a second battery for my music?

By the way, this is not for competition, its just for my personal use but I want it to sound loud and clear.

[ShadeTreeMechanic]

Does this happen with the car running down the road, or while idling, or with the engine off?

[crownvictoria31]

One thing I forgot to mention is that the 1/0 gauge power wire that I have running from under the hood is supplying power to both my amps right now which are the Lanzer and 600x4 fosgate. It goes to a fused distribution block 1/0 gauge in and two 4gauge out. I am running another 1/0 gauge power wire from front to back just for the Lanzer and giving it a 1/0 gauge ground aswell. Just wanted to put this in here as it might help you experts solve my issue.

[crownvictoria31]

Does this happen with the car running down the road, or while idling, or with the engine off?

I don't play music with engine off. This happens while idling at a light .

[ShadeTreeMechanic]

Replacing the battery under the hood would be a good start, but adding 2 or 3 batteries in the back would really help it especially after you add 3k subs. The problem with idling is the alt won't put out its max amps. A bigger alt will help and most aftermarket alts have a smaller pulley to increase the speed at idle. By adding batteries it would probably help a little but would just delay the problem you are having. Using more power from the batteries than the alt wil provide will just cause the batteries charge to go low. You would then need to drive around for a while to charge them back up. So the real answer is that you need more batteries and a bigger alternator.

[crownvictoria31]

You wrote that I would be adding 3k watts in subs? I ment to say that after adding subs, my complete system should be putting out 3k watts rms at most. So with this info cleared out, how would this all change?

[ShadeTreeMechanic]

You might only need one extra battery but you still need more alternator for idling.

[crownvictoria31]

So how would I do this. Which battery do you recommend for my trunk. I guess I can leave my stock battery in place then?

[Rich Schenk]

Even for a 3k system I would do biggest xs power Underhood that will fit. And I would do a xs d3100 or xs xp3000 and a h.o. alt. Did you do the big 4 and our all your grounds to frame?

[crownvictoria31]

As per big 4 i did positive battery to alternator with 250anl fuse. Battery positive to engine fuse box. Negative battery to engine block and negative battery to frame.