Core i3/i5/i7 improve battery life. How then is 13" MBp the winner?

[thinkdesign]

I assume that since all 3 batteries (MBp 13", 15", 17") are same tech. And I assume cubic inches of battery are proportional to watts. And larger screen size allows a similar enlargement of how many square inches of battery are in the lower case.

Now unless the 13" MBp's battery is somehow thicker... (nah, how could that be?) it seems that increasing a screen from 13 to 15 to 17" should, roughly speaking, allow the battery power to catch up. So, intuitively, the new MBp's 15" & 17" with the new chip associated with progress in battery life, should pull ahead of the 13" MBp.

But the 13" has the stated ten hour life, and the bigger ones, are rated at less. I must be missing something. How does a less efficient core-duo chip win the battery life competition?

 

[Hellhammer]

13" MBPs use Pxxxx CPUs which are rated at 25W. The CPUs in other MBPs are 35W and they come with discrete GPU which is 23W IIRC. The bigger screen needs more power as well. Apple said they chose killer graphics and battery life over iX CPU in 13" so it looks like C2Ds are more efficient. I'm too lazy to do some better calculations and comparisons right now, I may edit my post later on to add something better

 

[ozreth]

Wrong section methinks : /

 

[thinkdesign]

ok, so then why...

would a switch to Core-i in the Air mean a longer battery life, than the Core duo chip the Air now has. Or the slight bump if the Air caught up to the GPUoCPU combo in the present 13" MBp.

The screen size should more or less be "a wash", no?

Simplified math example: If 2 laptops both have batteries 1" thick, and in both laptop designs the battery's other 2, larger dimensions essentially match the vertical and horizontal dimensions of the screen, then if Design B doubles the number of square inches in the screen compared with Design A... Design B's battery will also have twice as many cubic inches of battery compared with Design A. i.e. -- If screen A is 50 square inches, battery A is about 50 cubic inches. Compared with screen B is 100 sq. in., Battery B is 100 cubic in. If the physical layout of the battery allows aprox. one cubic inch of battery for each square inch of screen... well, you see what I mean.

So if the laptop design inherently allows the battery to enlarge to proportionally keep up with screen enlargement... then the screen size should be close to a wash.... and something else, like the more efficient GPU-CPU should be the variable determining which gets more hours of life.

I've read in this Air forum many times... the opinion that Apple shouldn't put Core-i in the next Air (with no 2nd GPU, as there's no room), because the battery life gain would not be a big enough plus to offset the backsliding on graphics performance.

But I look at the example of the 2010 Macbook Pros, with the core duo 13" beating the Core-i-chip models by an hour in battery life... and I wonder "WHAT battery life gain?" would the Air get?" from changing to a Core-i chip? Meaning, could that imaginary switch be doubly disadvantageous? The only explanation I can imagine is... the 15" & 17" are battery rated based on idea that 2nd GPU is "on" some % of the time. Which would not apply to the Air. What battery life do the 15" & 17" get, if the nvidia GPU is never switched "on"?