Manufacturer Web sites list installers near you. All prices include installation, and federal incentives may apply.
Enginer (Detroit, Michigan)
2 kWh system: $2,500 ($3,500 in California for state-required certification and a 5-year warranty on PHEVs)
4 kWh system: $3,500 ($4,500 in California)
All-electric range: Approximately 1 mile for the smaller system
Max. speed in all-electric mode: 34 mph
Notes: Expect about a 50% mpg improvement. Not ideal for extended all-electric driving. Can be installed on first-generation Prius with some benefit, but not as much as second- and third-generation models. Kits for DIY conversions are available as low as $2,000.
Hymotion (A123 Systems, Watertown, Massachusetts)
5 kWh system: $10,500
All-electric range: About 15–20 miles (although the Hymotion system blends some gas usage with electricity throughout the driving cycle)
Max. speed in all-electric mode: Not relevant due to hybrid approach
Note: This is the only system that received “provisional certification” from the California Air Resources Board for emissions and is built to meet federal crash-test standards. Testing by national energy labs indicated more than 100-mpg performance.
Plug-in Conversions Corp. (Poway, California)
6.5 kWh system: $13,500
All-electric range: 10–15 miles
Max. speed in all-electric mode: 70 mph
Notes: Completely removes factory Prius battery and replaces with larger nickel metal hydride pack. Spoofs the Prius computer. Switch allows driver to turn off internal combustion engine.
Plug-in Supply Inc. (Petaluma, California)
5 kWh system: $8,000
10 kWh system: $12,000
All-electric range: 25 miles with 5 kWh system; 50 miles with 10 kWh system
Max. speed in all-electric mode: 52 mph
Notes: Fools the Prius computer with a switch to force shutdown of internal combustion engine.