Voiding the Warranty
Looking forward to my 30th high school class reunion this summer reminds me of a time when my car's engine was simple enough to work on with a crescent wrench and a pair of pliers, instead of looking like a prop from the latest Star Wars movie. I have fond memories of fiddling with my first automobile, a very used '65 V-8 Mustang. I mention this by way of establishing that my heart is with the folks who want to tinker with the way their Toyota Priuses use electricity, including the addition of a plug to recharge them from the grid. This sort of urge is what made this country great. And without innovators like this, providing a little external, unfunded R&D for Detroit and Yokohama, the evolution of cars would be slower than it is. But I must admit that I'm a little offended by the idea of someone charging $10,000 to add a plug and exchange the advanced nickel metal-hydride batteries of the Prius for a bunch of low-tech lead-acid batteries, just for the privilege of driving a few miles in pure electric mode.
I'm sure Toyota isn't kidding when they say this modification would void the warranty on these cars. Given the uncertain future maintenance needs of even a totally stock hybrid car, this risk should not be taken lightly. Notwithstanding the extra cost, swapping out the batteries and power controller (hardware and/or software) seems very likely to shorten the lifespan of of this very sophisticated and hardly inexpensive car.
Nor do the potential fuel savings justify this kind of investment, since $10,000 worth of gasoline at today's prices would take a factory Prius more than 150,000 miles. While it's true that a "plug hybrid" that was driven mostly short distances could stretch its gasoline usage to a truly remarkable degree--100 miles per gallon or more--the electricity it would use instead would be neither free nor non-polluting. The degree to which this would truly benefit the environment depends on the composition of the local grid power, which in many areas is fueled by coal.
Plug capability could make lots of sense for the next generation of hybrid cars, and I would encourage all of the carmakers to pursue this technology vigorously. But modifying an existing car that is already a paragon of fuel economy, greenhouse gas emissions reductions, and practically pollution-free driving makes little sense. It's a nice concept as an engineering prototype, but bad news for environmentally-focused consumers at this point.