the percentage discrepancy between the d2 and d2g is something that should be input as a bug on google code ... hopping over there right now ...
edit:
go here to report bugs/enhancements/defects to google:
android - Project Hosting on Google Code
must log in to be able to enter an item.
It might not be a bug and just how the phone handles the battery. I am not an expert on this but both phones can consider what is a full battery differently.