My personal wacko EE theory is that booting is not as strenuous as it seems at first glance, but does for some reason mess up the charge indicator/battery chemistry/power management in general, which in turn can/will influence possible runtime. I'm pretty certain it's not 'straight current draw' after losing 30% battery power on a N810 reboot (that would result in a serious meltdown if true ), and after gaining 7% on another (unrelated) reboot.