is it really nessary to have 2 batteries in your setup or just 1 good bat and alt and the big 3 be good enough

 

Depends on how big of a system you have. You can get away with a small battery. Or sometimes you need 2 big batterys, an upgraded alt, and the big three.

 

one of these
clarion DPX11500

1500W x 1RMS [2Ω@14.4 ≤1% THD+N]

800W x 1RMS [4Ω@14.4V ≤1% THD+N]
O POWER AMPLIFIER
S/N 72dB (Ref:1W into 4Ω)
and two of these
clarion DPX2250
CEA 2006 Power Ratings

200W x 2RMS [2Ω@14.4V ±1% THD+N]

125W x 2RMS [4Ω@14.4V ±1% THD+N]

S/N 69dB (Ref:1W into 4Ω)

 

All depends on what you deem necessary. While it may not be necessary, it sure is advantageous.

I recommend a second battery, wired properly and near the amps if possible.

More info? I've got a whack of old posts stored up, all relating to electrical... http://www.allstart.net/batadv.htm

 

I was running 1200rms this summer, and with the lights on, the interior blacklights on, and my stereo pumping. My battery was going dead while driving it down the street.
I would say if you you have the alt to keep up, you should be fine. Just test it out and watch your volt meter. If it doesnt stay up over 13.5 volts while driving, you should get a bigger alt.
If you plan on running the stereo with the car turned off, second battery for sure.
And the big three is always helpful.