I am charging my batteries right now. I use two in my grip. In warmer weather I have gone over a month before needing to charge my battery. Lately it has been less but that may be to my using Live View more often working on close up shots or the colder weather or that my original batteries are getting worn. I have my original Canon battery that is just over 3 years old now and a generic that is just under 3 years old. i have two replacements ready to go, one being a high capacity 2000 mAh while the rest are 1080 mAh.
I will admit I have never logged how many photos I have taken on a charge.
I do love how my camera feels with the grip on. It does feel more balanced. I picked up my sister in law's Nikon D5100 the other day and it felt odd (aside from it being a Nikon
). Not only did the 18-55 lens feel "front heavy" but the camera felt unbalanced overall without a grip. Not sure why she even has it, she upgraded from a D40 which felt better, she always shoots in full auto.