Maybe this goes without saying, but the % complete on any device is a complete fiction. The software is always making an educated guess, given that there are multiple variables at work. And then when you add even more power-saving technology, it really becomes useless. It's kind of like the Windows Experience Index - it's a number that maybe says something, but is mostly just a number.
So, I guess I', saying that the way to make the battery power level % more accurate would be to turn off all power saving features to make the system drain more linear. Then you would have a meaningful number, but your tablet would only last a few hours.