[Galaxy S II General] nrk_2k:
I understand perfectly about power consumption, I am trained in the electronics field. And yes you are right, your simplified power relationship doesn't work at all for a CPU. Main reason is that our phones use a DC power system, and voltage step down in a DC system is completely different to in an AC power system. AC power systems use transformers, which are extremely low loss, where as DC systems are relatively high loss comparatively. We must look at the current on the entire circuit of the CPU to the battery as the CPU itself doesn't draw all that much current, it is more of a controller of where the current passing through it goes. This is why current goes up and down depending on what the CPU is processing (what other components are drawing current through the CPU etc). That is why I query the extremely high "CPU" power consumption in the above diagram. This I am assuming is actually the power consumption of the CPU, GPU, RAM, CPU cache & Internal Storage. As anything that forces the CPU to work hard would have to be using all these components. And if current draw is measured at the battery, at not at each individual component, then there is no way to actually know what is drawing all that power. Our phones however are packed with voltage and current sensors, and applications can use these to display pretty accurate information about battery consumption. I am using one currently to do some testing and will post screen shots showing the results (Which are vastly different to the ones shown above). The other thing to mention is the fact that most of the power "usage" in a CPU would be loss due to heat. If the CPUs in our phones were subjected to 2-3Watts worth of heating at high frequencies, our phones would quickly get too hot to hold as the heatsinks would not be able to cope with that much heating. Try grabing a 3W tungsten light bulb after its been on for 10 mins and you will know what I mean. :D I think the screenshots I will post up of my testing (will be a few posts over the period of a few days) will show that the above diagram is not that accurate. Initial results show a lot more what I would expect of CPU power drain.\

Edit: Did a quick 4min 15sec 3D game test. CPU at 1200MHz for the entire time playing, screen on autobrightness (but not a full brightness) During that time, Hardware battery usage statistics were as follows: Screen - 84.57%, GPRS (2g data/SMS) - 8.75%, CPU - 3.77%, Radio (2g phone) - 2.92% (These percentages are the percentage of what each components drain was of the total battery drain) This pretty conclusively shows that the display is by the far the highest consumer of battery and that the CPU (even when working hard) is a one of the smallest consumers of battery (the CPU consumed only 4.46% the amount of battery that the display did). As you can see from this, it completely contradicts the above diagrams. (I will post screen shots when I am home from work)

Added Note:

After some thinking while trying to get to sleep, I thought I would clarify why the P = I x V model doesn't really work for explaining a decrease in current drawn from the battery due to undervolting. In a DC system, voltage and current are not "conserved" the same as in AC when changing voltage. In AC systems, a transformer is used for changing voltage, and due to this, when voltage is decreased, current is increased as power stays fixed. Whereas in DC systems, Power is not conserved during a voltage drop as the conversion is "lossy". In saying this, if the CPU did draw a 500mA current, the draw at the battery would be the same, regardless of the voltage being used at the CPU. As in a DC system, current is conserved and completely separate to voltage. So to sum it up, in an AC system, power is conserved, in a DC system, current is conserved.