% is not updated when screen is off on Gingerbread
This issue has been reproduced on Gingerbread 2.3.3 and 2.3.4 so far.
Tested on 2.2.2 and 3.0.1 without reproducing it!
It turns out that the % logged in the history is not updated when the screen is off! Though mV and temperature are accurately being logged!
This is a bug in Gingerbread, it has been reported to Google's team in Issue 18230 (http://code.google.com/p/android/issues/detail?id=18230).
Sorry for the inconvenience, I'm actively seeking a work-around.