Hmmmmm, I've heard of this "heat" story: on a blog , a tester show charging with 4.3V can do huge damage to the battery ,reducing seriously the ages of the battery.
And also I own a first generation iPod Nano and Video iPod, both manufacted in Nov 2005. Both of them was having "full charge" for every charge, but I can see obviously that both of them have only 80% battery capacity (As AAPL mentioned).So it's really a cell-story
It's the first time I heard "charging li-ion batteries from a lower power state introduces more heat than charging from a higher state". Intersting---------I used to think the voltage keep on 5V