I am using an after-market extended life battery for my 6700 that I got from this site that says it's a 3200mAh:
http://www.seidioonline.com/ I've had it for about a week now, and it's served me well so far. Although I haven't run it down past about 50% (yet) before recharging, I estimate that I could get at least 3 days usage from it, maybe 4 if I really stretch it. Of course, I may not be using it as heavily as you would, so your mileage may vary.