Use of EV mode
 

I have an 07 and 10 prius. the 10 has a ev mode but when i push the button it tells me that this function is not available. the manual tells me that i can use the function under 25mph. so i don't understand how to use the function. my 07 i get 54 mph to and from work the 10 is getting 56mph. these numbers are in the summer. i am in denver and in the winter the 07 drops to 49 and the 10 drops to 54 or 53. I'm happy.