Certainly makes sense (get it?), doesn't it. Nearly every EVO owner I know has, at some point or another, complained about the fact that their battery life drops about 5-10% as soon as they unplug it. Well, it turns out that's because of there's an overcharge protection chip inside Li-Ion batteries.
XDA user willy900wonka decided to tear his extended EVO battery apart, and lo and behold:
What I found was that a 8205 chip is used to provide protection and prevent over charging and over-discharging. Here is a quote from a google search.
S-8205A/B Series Applications-Optimized-Battery-Protection Circuits.
All contained voltage detectors are of high precision between 15mV and 100mV depending on the function.