batteries or caps?

WHAT?!?!

None of this makes ANY sense. 

From this logic a 40watt bulb put to three seperate batteries draws the same amount of current from each battery that it would require from a single battery!?!?!

Like you say - simple math - now I'm REALLY confused. . . . .

Hey!  When did I get an "I"????

When explaining theories you always try to assume everything is identical.  The drain (or bleed) characteristics of the batteries may be different which may make a small battery that can't hold a charge for very long appear to be leeching off a large battery with a long storage capacity.  If you have to identical batteries you can assume they will discharge at the same rate and you can assume that the voltage will drop from each battery at the same rate, so no leeching effect will be present.

The ESR of the system will be reduced by wiring the batteries in parallel, so you might actually see an advantage in that department.  The ESR deals with resistance of components in series - well when you double the capacity of the storage devices the resistance will drop (what happens if you wire two 8 ohm sums in parallel - you get 4 ohms).

Let me try to explain what I was getting at a little better above.  If you have a battery at 14vdc and another battery at 10vdc and you wire them in parallel you will have a 4vdc difference in potential.  The 14vdc battery will power the 10vdc battery.  As the 10vdc battery receives current from the 14vdc battery its voltage level will rise, while the voltage level of the 14vdc battery drops.

Eventually they will settle at ~12vdc, at which point there is no more potential (12vdc - 12vdc = 0vdc), and with out potential current can't flow, so you'll have the equivalent of an open circuit.

Not at all.  The lightbult will draw the same amount of current regardless of the device feeding it.

Say you have one battery with a storage capacity of 50A (not even the correct way to rate a battery, but it makes it much easier).  Say you have an alternator thats rated at 150A.  Now, assume the car and the radio together, at max load is going to draw 175A.  At first, you will be fine, as you have the 150A the alternator is providing and you have the reserve capacity of the battery (50A).  But, eventually you'll drain the battery, and you'll be left with only the 150A the alternator can provide.  At that point the car starts hesitating, the radio starts cutting off, etc. so you turn the radio off, dropping the load on the system to 100A.  However, in addition to the load of the car the battery, being drained, is now a load and will consume 50A to charge back up, giving you a 150A load on the alternator.

Now run the same scenario but increase your storage capacity of the battery by 3 (to 150A).  Sure, the system will play longer as it will take longer to drain the electrical system, but once you do drain it you now have to charge up a 150A load (three batteries in parallel) PLUS power the car.  So, at this point, even with the radio off you have the 100A that the car needs to function and you have the addional 150A that the batteries require to charge.

The point is that a battery that has less potential then the output of the alternator will be a load on the alternator.  The bigger the battery (ie the more storage capacity) the more power its going to take to charge it.

I'm trying my best here to explain it!

Okay - so by ur logic the idea of identical batteries is irrelevant - b/c they always 'equalize' - so why did you parentheically state "if they are idenctical" . . . ?

You'll be digging deep before I'm done with ya. . . . .

To cover my butt.  If someone mixes a Red top with a Yellow top I have no idea what would happen, as they use different cell technology.  Manufacturers are always saying that they don't recomend mixing battery types in an installation, and that is all I was trying to do.  Whenever using multiple batteries it is good practice to use identical batteries.

That, and who would ever buy two identical brand new batteries and try to prove me wrong?  :)

So you do have an isolator?  The isolator will prevent the alternator from seeing the entire load at any given time, which will reduce the loading effect, but require longer time to fully charge all batteries.

Do you have a single PAC200 isolating your main battery from your two additional batteries?