Extra Batteries

I remember reading awhile back about some one who had designed and installed their own additional battery array that the placed in their prius in the spare tire well. The had a sight with pictures and updates with mileage and such and said that surprisingly the batteries where lasting fairly well. I had wanted to check back there to see if the person added any more updates on his project/projects but can't seem to find the sight. I was wondering if anyone here knows what I'm talking about. When I read it last I do not believe the person intended to do any plug in charging of the pack, just adding extra battery capacity. Anyone know what I'm talking about/ have the URL? thanks.