Curtis Bratcher

Hi Everyone,
I'm the new owner, for one month, of a Magnetic Gray 2008 Pkg 6 Prius.
I have been getting around 40 to 45 mpg just doing normal driving, haven't touched the tire pressure yet.
On the way home from work yesterday, I reset the consumption screen and drove home 5 miles interstate and then 3 miles city street with 5 stop lights. During the 3 miles I usually run 35 to 40 mph and almost 100% electric. On the ride home yesterday, my mpg was 51.7. I assume that this was due to the interstate driving fully charging the battery, so that I was able to run 3 miles on electric, yielding a higher that normal mpg. Also, I try to hang back from the other drivers and slowly coast to the traffic lights and thereby charge my battery for additional electric driving.
On the voice activated navigation. It doesn't work very well for me. I have a southern accent, so I assume the it doesn't hear my voice correctly. Is there a way to "train" the system to hear my voice?
One other question. Does anyone know what the cost of replacing the hybrid battery is? I don't worry about it since it is warranted for 8 years, but people ask me and I want to know. My dealer didn't know because they haven't had to replace one yet. One friend had a ford hybrid and it cost $4000 because it was out of warrantee. I would guess that in 8 years, a better and more efficient battery will come along anyway.