The gist, converting a Prius to become a PHEV can be done. Companies, such as Hymotion have kits that can transform your Prius into an PHEV. What are the pros and cons?
Pros. Obviously, you can extend your mileage but again, it depends on many factors, how you drive, where you drive and the condition of traffic.
Cons. Extra weight, and fuel economy goes up once the batteries are depleted which cannot be recharged with the gas engine, as in the case with the Hymotion kit.
Consumer Report’s, CR, February 2009 issue had some interesting points. First, some Toyota dealerships can do the kit conversion. Second, the warranty isn’t necessarily void, and in some cases Hymotion says they will pick up where Toyota leaves you. It’s a case by case scenario.
The numbers, CR’s fuel economy was 67mpg instead of 42, with peaks of 87. The added 187lbs battery weight lowered the maximum load capacity to 623lbs. The spare tire is strapped inside the trunk, with less cargo. This means the conversion could be good if you travel alone, or with 2 or 3 people for less than 40 miles a day, unless you can recharge here and there. You could theoretically drive on electricity alone, that is for about the first 37 miles. After that, the fuel economy goes down to 40mpg, due to the added weight and depleted batteries. Factor in the recharge time of 6 hours and money spent, on an average 11 cents per kWh, and you get 53 mpg, average.
Two question that automatically pop up in our minds are that different drivers will get different results and that there could be a way to recharge the batteries using the gas engine, maybe in the near future. Interesting conversion given the warranty issues are somewhat answered and that someone with a light foot who can recharge anywhere could feasibly extend their MPG to well over 100.