Old iPod battery measurement technique

Hi,

My girlfriend and I were having a discussion regarding how the old clickwheel ipods measured battery life. If you guys remember, sometimes the battery icon on those old ipods went up as if they had magically gained juice.

I argued that the icon measured an absolute value and that the reason for the fluctuating battery levels was that the ipod was slightly inaccurate when measuring the battery power left. Thus it sometimes reported higher levels and sometimes lower levels.

My girlfriend argued that the icon measured the relative battery time left i.e. if the ipod was doing something more strenuous the battery icon would go down indicating that it wouldn't survive for that long, while easier tasks resulted in the battery icon going up as it was indicating that it would last longer relative to the power drain.

Who's right?