It is disturbing that there are people out there who can't understand this VERY BASIC engineering.
Voltage, by itself, has NO MEANING. You are forgetting about CURRENT. POWER = CURRENT x VOLTAGE.
Battery drain is DIRECTLY PROPORTIONAL to POWER. Not voltage. Double the voltage and half the current, power remains the same.
Dual core does NOT increase battery life. It increases PERFORMANCE by ***DOUBLING*** the physical processing units.
Battery life is increased through MINIATURIZATION and SIMPLIFICATION, which becomes *EXTREMELY* important as you increase the number of physical processing units.
It is the epitome of IGNORANCE to assume that there is some relation when there is not. The use of multiple cores relates to hard physical limitations of the silicon. You can't run the silicon at 18 GHz! Instead of racing for higher frequencies, the new competition is about how much work you can do with the SAME frequency, and the ***EASIEST*** way to do this is to bolt on more cores!
For arguments sake, take a look at a couple of processors;
Athlon II X2 240e / C3.... 45 watt TDP, 45 nm
Athlon II X4 630 / C3.... 95 watt TDP, 45 nm
Same stepping, same frequency (2.8 GHz), same voltage, same size, and the one with twice the cores eats more than twice the power. Wow, imagine that!
The X4 is, of course, FASTER, but not by double.
Now lets look at another pair of processors;
Athlon 64 X2 3800+ / E6.... 89 watt TDP, 90 nm
Athlon II X2 270u / C3.... 25 watt TDP, 45 nm
Different stepping, SAME frequency (2.0 GHz), same number of cores, different voltage, different SIZE, WAY different power consumption. JUST LOOK how much more power the older chip eats!!! 3.56 times as much. Also note that other power management features exist on the C3 that didn't exist on the E6, so the difference in MINIMUM power consumption is much greater.
Conclusion: There is no correlation between a reduction in power consumption and an increase in the number of PPUs. More PPUs = more performance. Reduction in power consumption is related to size, voltage, and other characteristics.