2010 Plug-in Prius Prototypes – Click above for high-res image gallery

It's been two-and-a-half years since we last got behind the wheel of a plug-in Toyota Prius. The name is the same, but today's plug-in Prius is a totally different vehicle, and it was high time to see what changes Toyota has made to their plug-in hybrid (PHEV) in its ongoing effort to slowly get the car ready for the U.S. market.

Back in late 2007, the prototype had a NiMH battery pack and the converted vehicle was based on the second-generation model. The new fleet of PHEV Priuses in San Diego this week as part of Toyota's Sustainable Mobility Seminar are converted 2010 third-generation models, featuring upgraded lithium-ion packs.

Toyota has brought the PHEV Prius fleet to the U.S. to begin a two-year test and monitoring period. The vehicles are equipped with transmitters from Qualcomm that record not only driver behavior, but also how often the car is plugged in. We'll have more information soon with technical details about the mules and an explanation of Toyota's plans to test and sell the long-awaited plug-in hatchback for 2012. But before then, we wanted to grab some seat time.

The short version is that driving a plug-in Prius is almost exactly like driving a standard one, except that it remains quieter for a longer period as the engine is off more often (during short distances) thanks to a larger battery pack and improved all-electric performance. Acceleration, handling, braking – everything feels awfully familiar. Make the jump to find out more, including how you can now go up to 64 mph without using a single drop of fuel.

Photos by Sebastian Blanco / Copyright ©2010 Weblogs, Inc.

Sixty-four mph was the highest speed we managed to achieve while staying in pure EV mode, and it turns out that most of our two, 10-mile loops were completed using battery power (we managed 70 percent on the highway loop, then 83 percent on the city loop when we started with a full pack). The newest PHEV Priuses have a maximum all-electric range of around 13-14 miles, compared to the seven miles in the plug-in version of the second-gen Prius.

In the new models, driving on all-electric power is indicated by a green car image that says "EV" in the driver information screen (see below). If the engine kicks in, then this picture turns to a simple, empty outline. This is useful, because when you're traveling at highway speeds, you can't always tell when the engine turns on. When you're driving in quiet locations, then the engine is noticeable, but other than that, the EV light is your only signal that you've moved from electrons to dead dino-juice.

This all reinforces the impression that the new plug-in Prius is just a more advanced version of the regular car you can buy today. You start the car the same way (but now the button is a nice blue color) and shift and steer just like always. The plug-in even has three driver-selectable modes – Eco, Power and Standard – that are similar to the options in the third-gen Prius (there, though, the choices are Eco, Power and EV).

The main feature of Eco mode in the new PHEV Prius is that the pedal becomes more physically difficult to depress, and so the throttle is opened at a smoother rate during acceleration. In practice, this makes the go pedal less responsive, which will annoy anyone who wants to speed away from a red light – an unlikely scenario for the average plug-in Prius owner. In any case, when you really push the pedal down, then the charge/power bar moves all the way into the red on the right side of the screen. This is a visual cue that should be quite familiar to anyone who drives a standard 2010 Prius. Noticing a trend?

Except for the few seconds it takes to plug and unplug the car each day, the current version of the PHEV Prius is the regular Prius, just with better fuel economy. How much fuel does it use? As with all plug-ins, the answer depends on how far you drive each day. For us, on our short routes, the info screens in our test cars read 99.9 mpg. If we had driven much further, we would undoubtedly have seen a serious decrease as we exceeded the car's EV range, but we imagine drivers can expect to get mpg numbers easily in the upper 50s on most days. Thanks, batteries. By the way, those cells take around three hours to top off from a standard 110 outlet and each vehicle comes with a chargre unit that plugs into a standard outlet and feeds the car juice through a J1772 connector.

What else is different about these cars and the regular 2010 Prius? Well, these models have the PHEV-specific blue mica metallic paint color, the trunk floor is raised up about two inches ( see here) to make room for an extra 220 pounds of batteries and there are some cooling vents under the back seat. The batteries are in one pack, but are divided into three modules. One module is for the standard hybrid system, while two are dedicated to the EV drive. We don't quite understand why Toyota felt the need to separate the pack into three parts, but asking some questions about this setup is one of many things at the top of our list once we get to spend some time with an engineer. Stay tuned for that, and more.

Photos by Sebastian Blanco / Copyright ©2010 Weblogs, Inc.

Our travel and lodging for this media event were provided by the manufacturer.

Autoblog accepts vehicle loans from auto manufacturers with a tank of gas and sometimes insurance for the purpose of evaluation and editorial content. Like most of the auto news industry, we also sometimes accept travel, lodging and event access for vehicle drive and news coverage opportunities. Our opinions and criticism remain our own — we do not accept sponsored editorial.

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