For those who travel very short distances, the Toyota Prius Plug-In could almost be thought of as an electric car. With a battery pack that's about 5 kW-hr—many times that of the standard Prius—it can, within reason travel at highway speeds on electric power alone, or up to 14 miles or so as an EV.

Not quite, actually, but almost. First, you only have an EV as long as you're willing to watch the dash displays and not press on the accelerator too hard; and second, even if you're really careful about driving style, and even if you have the Plug-In switched to Eco Mode, the gasoline engine turns on for periods.

It is a little puzzling as to why even in EV Mode the gasoline engine needs to run periodically—sometimes for many minutes. Three of the four 'cold starts' we've done in the Prius Plug-In have prompted the gasoline engine to come on.

EV button would let you ration battery power

But for that first issue—the gasoline engine coming on when you need to press harder on the accelerator—the regular-production Prius Plug-In that will be available for purchase next year will get one useful feature our test car doesn't have: an EV Mode button that lets you lock out EV Mode and run as a normal Prius. That way, if you have a long mountain pass, or a higher-speed stretch on the Interstate, you won't quickly burn through the electric range, and could instead save it, for instance, for some lower-speed suburban driving.

All Cars Electric is fortunate to have, for a week, a Prius Plug-In to test, and we're starting to rack up some observations on what life with a plug-in hybrid would be like. Over the first nearly three days, we've done one partial charge and two full charges, and covered a total of just 38.4 miles.

As you might guess, most of that distance has been covered in the Plug-In's EV Mode, which engages automatically when you start the car and stays on until the larger battery pack is exhausted. From our two full charges, we've seen close to 12 miles from a charge, but we've yet to drive it only in very slow-speed city driving, where the EV Mode would likely shine.

The uncalled-for starts of the engine are still perplexing, and in a few cases if we knew they were coming, or going to be so long, we would have driven in a different manner. In our most recent cold start, the engine started for four minutes in all (and the first mile of driving at low speed). And moving along at about 55 mph with traffic, the gasoline engine came on for about 90 seconds, beginning just after cresting a gradual grade (with the battery only about half depleted).

98 mpg so far

Toyota Prius Plug-In Hybrid prototype, tested in November 2010

Toyota Prius Plug-In Hybrid prototype, tested in November 2010

That said, we've gone 38.4 miles so far and averaged 97.8 miles per gallon (plus about 2.5 charges) with what we'd consider a normal Prius driving experience. That's extremely impressive.

With many more miles to cover over the next several days, we'll keep you posted, and we'll do our best to keep the Prius charged up.