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Fairfax County, Virginia Adds Hymotion Plug-In Prius To Its Fleet

by Jack Rosebro

Virginia’s Fairfax County Department of Vehicle Services, which already has conventional hybrids in its fleet, took delivery last week of a Toyota Prius PHEV conversion from Hymotion of Toronto, Canada. The vehicle is part of the county’s regular motor pool, and is available to employees traveling on county business.

The Hymotion L5 conversion kit features a 5 kWh lithium-ion battery pack that supplements the OEM NiMH battery pack in the Prius.

The PHEV system recharges from the engine and regenerative braking during operation and from the power grid when the vehicle is parked and plugged in. Once the PHEV battery is depleted, the vehicle resumes normal operation using the factory battery. While the PHEV battery is in use, the OEM battery fuel gage indicates its status.

Fairfax County’s Board of Supervisors voted in June to join Plug-In Partners (earlier post), a nationwide initiative to encourage automakers to develop and produce plug-ins. According to James Gorby, director of the county’s Department of Vehicle Services, more than half the cars in the United States travel less than 25 miles on most days.

Hymotion’s engineers completed the conversion on the evening of Tuesday, 28 November. Dave DuVal of Fairfax County drove the vehicle to attend the Electric Drive Transportation Association conference in Washington, DC Wednesday and Thursday.

With some highway and some city miles, the Prius display shows that with 94 miles driven, the car has averaged 77.9 mpg, starting on its third battery discharge. We like it so far!

—Dave DuVal

Hymotion claims that the L5 pack can double the fuel efficiency of the Prius, pushing it to more than 100 mpg in combined city/highway driving, depending upon the actual drive cycle.


Bud Johns

I wonder if they also gave it the all electric mode like in europe, where the engine doesn't have to crank and warm for emissions sake. I have a kit that does that, but didn't install it for fear of warranty problems. Anyway, if you took it easy on the accelerator, you could drive a number of miles without the ICE ever cranking!

George K


Yes. These two dozen PHEV conversions utilize the EV code in the Prius drive system in order to keep the ICE from firing up when it’s not wanted, below 34 mph. Check for best ways to use your EV button.

I got mine from Coastal. The first time I tried it, I felt the “thrill of victory”! Driving in pure electric mode is smooth, quiet, non polluting, not to mention it’s a real kick!. After a short while a second set of thoughts entered my mind… I NEED A BIGGER BATTERY! I believe that is the same thought process that Felix Kramer of went through, which gave him the idea of the PHEV Prius, years ago.


Depending on where you get your electricity, this PHEV may be a good environmental (GHG) proposition. Cost per kWh electric is another consideration. At $2.50 ga/reg gasoline, $0.25 kWh is a good deal. Those who get the juice for $0.1 kWh, that is roughly equivalent to $0.90 ga/reg. It is even better at $0.06 kWh, ~$0.54 ga/reg.

Bud Johns

Thanks, George K. BTW, even if you have to accelerate rapidly the ICE only runs when needed for the extra punch, then shuts down. I used to live in Florida, and the ICE usually cut in around the 36 mph, but we moved to the mountains in Tennessee, and the engine is off even at interstate speeds on a proper slope as the battery REALLY gets a charge....we get our best mileage here ever. About 56 mpg town, 51 highway


I am one of the first people that would purchase a reasonably priced plug in hybrid. Due to the high costs of the batteries, the price of conversion is still too high for wide spread adoption.
How much did this car cost Fairfax County, Virginia?
If it is in the range of $25,000 or more to convert the car, how do the taxpayers of Fairfax, Virginia feel about funding this effort?
I realize that it will be used to help promote PIHV, but should taxpayers be paying for it? Or was this car purchased through donations?


I seem to remember reading somewhere (probably here) that the hymotion conversion was arround $10,000

kent beuchert

I see the charge is about the same as another company. The problem here is that $9500 voids your Toyota warranty, provides 5 Kwhr capacity, which costs them approximately $2000. If this isn't thievery , I don't know what is. Those people who buy these things probably are people who think the oil companies are screwing them. That's not who's screwing them. The gas bill for a Prius at $3.00 per gallon and 12,500 miles per year is less than $1000. These batteries will need replacement probably every 2 years or so. So the cost of batteries roughly equals the cost of fuel, but look at the overhead of installing these batteries and tweaking a computer chip. Economically, this sucks. If they sold a kit and held down their greed to only a profit margin of (only!) 100%, it might be half worthwhile, at least for guiltridden anal types' peace of mind.


Kent, it's early days for PHEV, so it's naturally going to be expensive.

We need early adopters like these to bring the costs down, and then the masses (and the manufacturers) can have them at mass-market costs.


I don't know specifically what batteries they are using but LiIons will NOT need replacement in 2 years. Should be more like 5-10 years, depending upon type and usage.


Cost of gasoline will mean nothing when you can't get it or its rationed - or New York has sunk under higher sea levels.

What would be the net present value of the investment required to plant a swamp forest the size of Saudi Arabia, bury it in sand and leave for 100 million years, at compound inteest of 5% p.a.? That should give you an idea of the true "cost" of gasoline. We live off the bounty of Mother Nature and pay her back with two fingers.

Go ahead and put dollar bills in your gas tank when gas is rationed to 4 gallons a week.

Christopher Hogan

I've been looking at getting a PHEV conversion for my Prius, from one of the commercial offers. Hymotion appears to be leading the pack, but the battery life issue is definitely holding me back. Of the three firms who have announced plans to offer PHEV Prius conversions in the US, Hymotion is the only one offering a battery warranty at all, and Hymotion's is only 2 years. Looking at the specs for the batteries they use, they may last as little as 1000 discharge cycles on average, which would be about three years of daily use. But other batteries in production now appear to have much longer lifetimes (google altairnano and Phoenix motorcars, to see that there is a California startup constructing pure EVs using the new altairnano Li-Ion cells, and that the specs for these cells suggest they would be a true life-of-the-car battery. So, my take is that a) this is a wonderful idea, b) it's not cost-effective yet, but (largely) so what, c) I don't want a dead 160 lb li-ion battery in 3 years, and d) I'm sitting on the sidelines for a bit longer, waiting to see what happens nex


I understand these negative opinions I'm reading are anyone's to post but please give plug in hybrid cars a chance.

I hope for better batteries and I believe they already exist. I wish they left the EV button functional too. Some folks will go to any length to keep things the way they are. Relaxing C.A.F.E. standards and forcing Toyota to remove the EV mode for the American Prius is just one of them. Offering nice tax incentives for business owners if they buy an extra big truck is another.

Don't wait for pie in the sky promises from the Government and American auto manufacturers, buy a Prius today and they will get the message.

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