Not sure how it will work with the D2G, but I had the D2 extended battery for my D1 and I could get through the whole day fine without worrying about needing a charger. I did a lot of web browsing, texts, less than 20 min in calls probably, and 2 email accounts sync. It was worth it, especially since I got it for $26 and change.
Btw, you'd get more responses if this was in the right forum I bet.