Stealth Mode

When the vehicle is turned-on with the "start" button, it is ready to drive immediately with the electric motor, while electric pumps warm the engine with previously saved hot engine coolant, before the internal combustion engine is started. The delay between starting the car and starting the internal combustion engine is approximately seven seconds. The Asian and European versions of this vehicle provide a button labeled "EV" that maintains Electric Vehicle mode after startup, under most low-load driving conditions. The North American model does not have the "EV" button, although the "EV" mode is still supported internally by the Prius high-voltage management computer. While some have speculated that EV mode was not included on North American models in the interest of retaining the warranted battery life of 100,000 miles (160,000 km) in the US—150,000 miles (240,000 km) in California and several other states—engineers note that EV mode is automatically overridden when the battery requires recharging from the internal combustion engine. The Prius is designed to protect the battery from extreme discharge as well as over-charge and will utilize the engine as-necessary to maintain the optimum conditions for a long battery life. In addition to information at online discussion groups, the PRIUS+ Project offers instructions for do-it-yourselfers who wish to enable the button, and after-market components provider Coastal Electronic Technologies offers a kit. Several aftermarket vendors are supplying OEM EV buttons for 04+ Prius.

Extra batteries

Evolving from the button project, The California Cars Initiative (CalCars) converted a Prius in 2004, adding larger batteries, and private companies EDrive Systems in the United States and Amberjac Projects in the United Kingdom announced plans to sell conversion kits in 2006. The most recent versions use a new, patented advanced safe-format Lithium Battery from Valence Technology (VLNC, NASDAQ) called Saphion. The energy density and far more efficient utilization of these batteries provide around 20x the available power of the standard NiMH battery pack but at only double the weight. Tests show it capable of achieving >30 miles in all electric mode at speeds below 34mph. The internal combustion engine starts only at higher speeds or when extra acceleration is needed. Fuel economy (as demonstrated for several journalists) is improved to 100-160mpg source article depending on driving conditions. City driving may be possible without using the gas engine at all, eliminating the use of almost all liquid fuel in exchange for electrical energy.

Chargers

CalCars initiated efforts to promote the idea of plug-in hybrids to be built by automakers, and documented the emissions benefits of plug-in hybrids not only on California's clean power grid but also on the national (50% coal-fueled) power grid. This addition would be relatively ineffective without additional battery capacity or reprogramming to more completely discharge the batteries (which would be detrimental to their service life.

Recently Toyota has announced that it intends to build a plug in hybrid vehicle at an unspecified future time.

Solar Panels

Solar panels provide additional energy to the batteries while the vehicle is in motion or otherwise away from the grid. Solar panels are also useful when the Prius is parked for extended periods of time in a sunny location if it doesn't have a charger or is not connected to a power outlet. Some drivers have claimed up to 10% mileage improvements with the addition of their solar panels, while final results are dependent on the size and efficiency of the solar panels as well as weather conditions. Drivers in Australia and the southwestern states for instance, see the most mileage improvements on their Prius. One advantage of solar panels is that they do not wear out or depreciate like ICE components.