Do You Regularly Drive in Mountains?
The Prius will not climb very steep hills indefinitely.
One aspect of the vehicle's design that drastically improves economy and reduces emissions is that the engine is not sized for the peak power demand. When heavy acceleration or steep hill climbs are called for, MG2
provides a boost to meet the performance needs using power from the battery. Although heavy acceleration can't go on for very long and the battery gets a chance to recharge, in some parts of the world you can find steep hills long enough to drain the battery to its lower limit. At this time, you have only the ICE power to run with and you'll be forced to slow down.
You'll still make it to the top. People have driven to the top of Mount Washington, which averages a 12% grade for more than seven miles. But, after the battery power is gone, the maximum speed (according to my calculations) will be about 40 m.p.h.
Not being able to climb Mount Washington at 60 m.p.h. is, of course, no reason not to choose a Prius. But, if your daily commute happens to be over the California coastal range or some other long steep hill, joining the trucks in the extra slow lane might wear a bit thin after a while.