2 car batteries?

You say you are an electrician in your profile and you can't comprehend this?

So tell me what impedance your two 12" DVC 4-ohms speakers are presenting to the amp.  Now tell me what impedance the two DVC 2-ohm speakers are presenting to the amp.  Lets' see: DVC 4-ohm loads wired in parallel at the speakers creates a 2-ohm load, and wired in series creates a 8-ohm load.  How are these wired and how are they wired to the amp?  Each DVC 2-ohms speaker wired in series presents a 4-ohm load.  How are these two wired to the amp?  Are the two sets presenting the same net loads on the amp?  No?  Yes?  You tell me.

If the load from both sets of speakers is the same, and if the volume level on the receiver is the same, the current draw from the amp will be the same.  So, in your case yes I agree "something else" is certainly happening, and by something else I mean it ain't the same load in both cases.

No, speaker size is NOT relevent.  In your specific case, it is, but I have seen 10" subs with higher power ratings then 15" subs, so to solely base power consumption off speaker size is impossible.

You need to analyze each case individually and base your design off RMS power of the amplifier(s) and the type of amp(s).  The amount of power output and the efficiency of the amp will ultimately determine how long a battery will last.

ianarian wrote: I hear ya Dyohn. But I know what Im talkin about, its all yall that dont get it. No, what I meant in the beginning was: I've seen less than 500w push that 12 just fine. However their L7-15's and solo 18's are not as forgiving. Now my 15's can be replaced with 8's and still be able to have same effect on my battery that I was talking about. When I was referring to speaker size, it was based off the fact that this guy's L7 can be ran fine on a good battery without changing alternators and a bunch of other things like that. Anything bigger than a 12 I would not recommend to take any shortcuts on power.

And that's not a fact, it's just wrong.  The size of the speaker has nothng to do with the load it will place on your electrical system.  It's the amplifier that does that, and the load placed on the amplifier by the voice coil impedance.