I found the statement below in another post to explain the difference between 2010 level I vs II. My question is: for someone who just drives highway miles and is interested in maximum HV battery life would Prius I offer an advantage over Prius II since there would be no need for EV-only mode for highway driving, and by not having EV-only mode would this extend HV battery life? Toyota spokeswoman Ming-Jou Chen said while the better-equipped, mid-level version will make up about two-thirds of Prius sales, the so-called "Prius I" base model "will be out there." She said it will lack these features standard on other Prius models: Cruise control, rear wiper and EV-only mode that keeps the car operating on battery-only as long as possible. It also will lack the "touch-tracer display" that shows on a screen what the driver has adjusted using steering-wheel controls, meant to minimize the need to glance down.
EV mode is unlikely to play much of a role in highway driving, since that's usually at speeds the gas engine needs to be on for with the current Prius. I don't think you'll see any real difference in longevity of the battery pack between Prius I & II.
EV only mode would mean the "button" on the console. Operationally, you could still trigger it in the same fashion as the current gen w/o the button. Those who use EV mode appropriately shouldn't adversely affect battery life. Those who abuse it and force the car when it's not really economical may experience otherwise.