It won't show 100%, usually I get 96%, sometimes 97%.
There's an app called batlevel which is a widget to show battery level. But this one you need to adjust it's refresh rate to conserve battery. It's not so stable for me cause sometimes it never refresh then I notice it has stop responding, have to close it and re-open.
For lower resource version, use Desktop Command Execution Widget. This widget allow you to execute X-Term command. It already come with preset few commands, like Battery Level in % and mah, Internal and External IP, etc.
If you leave you phone to charge until next morning, the full bar battery is not accurate. (e.g. maybe showing 96%)
This full bar will drop very fast to it's accurate % quite fast.
This is because... I believe there is a cut off when you battery is full and you leave it on to charge for long time. So, it will not charge your battery until you battery drops to a certain level (I think below 85%, then it will re-charge).
If you try to charge you battery when you battery level is above 85%, you cannot charge, it will tell you the battery is full.
If you charge your battery till full and unplug, the 96% or 97% is accurate version and it will not drop fast this time.
thanks alot PROFESSOR ANDY.