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Public Conversion of Prius to PHEV With Nilar NiMH Pack

Attendees at the upcoming TechMesh 2007 conference in Boston will be able to see a team of volunteers lead by CalCars perform the live conversion of a Prius into a plug-in hybrid (PHEV) using a 6.4 kWh NiMH battery pack from Nilar.

Founded in 2000 and with facilities located in Stockholm and Denver, Nilar developed a patented membrane technology for bi-polar batteries that it claims has enabled performance breakthroughs surpassing the standard NiMH chemistry in terms of power density, weight, and volume.

Based on years of experience in battery development and production, we set out to re-engineer the battery to remove common failure modes and construction limitations that plague existing high performance batteries. We focused on reducing the internal resistance, not only at the cell level, but in the complete battery pack. Our new construction approach provides lower internal resistance, uniform voltage and temperature conditions, and good heat transfer. This allows us to produce a very long cycle life battery with superior power and energy density. Newly developed automated production equipment provides consistent quality at a competitive cost.

—Neil Puester, Nilar Co-founder

Nilar stacks battery cells in series, with a conductive membrane between adjacent cells, acting as a cell wall and the electrical connection. The anode of one cell contacts one side of the membrane and the cathode of the adjacent cell contacts the other side. This results in negligible transportation resistance of current between the cells, and uniform voltage across the entire electrode.

The basic Nilar battery module is a 24V, 9Ah unit with nominal power density of 277 W/kg and 560 W/liter. According to CalCar’s Ron Gremban, the Nilar pack will provide about 20-25 miles EV range in a Prius and weigh around 104 kg (230 lb), with an expected cycle life of up to 2,000 cycles (6 years of daily use) and an expected cost of $6,000-$7,000.

In August, Nilar announced a partnership with Plug In Conversions Corporation of Poway, California, which provides PHEV conversion services and support for DIY converters. Plug In Conversions Corporation is also an exclusive distributor of Nilar batteries for Electric Vehicle (EV) applications.



If the cost of these batteries can be reduced this might be an option worth considering when the original Prius batteries need to be replaced.

This also might also give Toyota a second source for NiMH batteries without the restricts imposed by Cobasys.


This is great, why wait for Toyota to do it and do it poorly (8 miles plug in range)?


why wait for Toyota to do it

Says a guy who just told us that solar is not afforable because it has a multi-year payback period.

But hey - drop $20K on a Prius, another $10-15K on an aftermarket plug-in kit, and void your Toyota warranty. Great idea!



Aah, it says $6-7k not $10-15k.

hampden wireless

We have seen alot of PHEV companies make great claims then not deliver. The trail of dead or non performing companies is at least three now. (non performing to me is saying cars will be publicly available in 2006 then not even having any done for the general public in 2007)

This offer sounds great but now I am skeptical. I would drive hundreds of miles for installation and gladly pay $7,000 for a 25 mile range and a safe system.


Aah, it says $6-7k not $10-15k.

Doesn't change the substance of my comment, chronic niggler.

Solar's not affordable! Get a PHEV now! Spend a bundle, void your warranty! I know it makes no sense, but I'm a simp who's concluded that the one and only solution to life is battery cars and radioactive energy. Economics? Never studied it! Never left my parents' home!

My name? Benji.


You could always get a used Prius (warranty already expired or close to it) for less money and put the battery in it, If the battery outlasts the car, take it out and put it in another. The car itself will last longer when the engine gets less use.


The pack's specific energy is still only 61.5 Wh/kg

(6,400 watt-hours)/(104 kg)

This is still far below lithium ion's lowest offering.

Roger Pham

Okay, so now we have $6000-7000 USD for 6.4kwh, or roughly $1000/kwh for 2000 cycles, meaning $1000 /2000 kwh battery amortization cost, or 50 cents/kwh. Adding to that 15 cents/kwh utility rate, or 65 cents/kwh overall energy cost, and since a Prius is capable of ~250wh/mi, or 4mi/kwh, so the energy cost per mile is 65 cents/ 4mi = 16 cents/mi.

A gasoline Prius costs ~280 cents /50 mi (@ 50 mpg), or a fuel cost of 280/50 = 5.6 cents/mi. If this Prius is run on potentially-renewable natural gas costing 1/2 that of gasoline per BTU, then the cost/mi is only 2.8 cents/mi.

Still, very encouraging and exciting development, given such a high volumetric and gravimetric energy density, ideal for HEV's. This will open the door for more affordable HEV's to come. The day will come when all cars will be hybrids, when electrical components will be more affordable.

Roger Pham

"The pack's specific energy is still only 61.5 Wh/kg" : AES

This is a complete pack, probably with all the built-in cooling mechanism and protection mechanism, whereas A123 Lithium is rated at 130 wh/kg but perhaps barebone battery only, without other necessary hardwares?

The Prius' 1.3-kwh battery pack weighs ~40kg, or only 32wh/kg! So the Nilar has twice as much wh/kg, but wait... the Prius' battery is capable of 21kw /40kg, or ~525w/kg, twice as much power /kg as the Nilar at 277w/kg, and costing ?$1000-2000 USD? or comparable per wh of capacity. So, the trade off here is power over capacity, and higher power per $$ in cost.


Per Roger, this doesn't come close to making economic sense with $3.00 gas.

Jack Rosebro

Folks, when you do your calculations, keep in mind that the 6-7K projection is for the battery modules alone. A PHEV will also need a control board, a charger, a cooling system, and installation of all components.


Roger, Nick: Agreed that at 3$ gas the economics aren't favorable. But how long will it be before the price of gas goes through the roof (if you can get it at all)?

Roger: You might want to revisit your amortized cost of the battery/kwh when you consider two things. First, the 2000 cycle rating is for deep cycles. If you don't deep cycle your battery you will get significantly more kwhs out of it (yes I know that reduces the effective range). Second, the remaining battery still has residual value even after 2000 deep cycles.

Interesting technology, but limited by its use of Nickel.



The performance on this NiH batteries is only stated in W/kg (or W/L) whci his a measure of instantaneous power, a 130 wh/kg lithium ion is a completely different measurement: what is the w/kg of a A123 battery?


Sorry I didn't mean to misspell your name, if I wanted to make fun of your name I would have gone with "jackas...". but what does nuclear energy and the price of solar have the do with a Prius upgrade?


thats exactly 1000$ too much for me (and future diesel hybrid driver),

in a gasoline hybrid car here in italy you will already save money,
but with a diesel car not;

with my driving pattern,
gasoline here at 1,30 Euro / liter ~4,5$/gal,
65 km that i make daily to my work

i will save with a prius and this pack ~2,6 Eur in gasoline cost. (instead of 3,8 (0,65 * 1,3 * 4,5) i will pay 1,2 Eur for my daily trip to work.

this 2000 times (maybe even more with less capacity)
and i save over 10 years 5200Euro in gasoline cost (6700$)

and you lucky americans with lower price for electrons and higher consuming cars could save even more


2-3kwh more for this system at the same price and we are there


I think the problem this forum is that the majority of the contributers
appear to be obsessed with the cost of taking enviromental measures
in our lives.
As a individual who has invested in this types of technology to try
and reduce my impact on the planet , I can tell you that there is a sense
of well being that comes with it , ie hot showers at little or no carbon cost,
due to an efficient solor hot water system , a steal at 4000 euros to heat
360 litres of water from april to october ,without using any boost.
The more of us that can afford to invest in these emerging technologys
the cheaper they will become for everyone .
Ok a prius with a 6kwh battery may cost 6 or 7 k more than the std model,
but just borrow a little more to buy it , it will only hasten the arrival of
this type of car for everybodys budget , and thats got to be a good thing.

bruno cipolla

Correction: euro (italian) gasoline price is about 6.7$/gallon.

3.79 liters (one gallon) times 1.3 euros (price per liter) times 1.36 (today's $/€ conversion rate)

other euro countries prices not much different.

Euro gasoline price more than twice US, Euro average gas consumption (lt/km) about half US. That's it.
Btw Ialian electricity price outrageously high, 16-18 Eurocents/KWh i.e. .22-.25 $


Fine idea and sounds like a good product. Where can I receive one?


in my dreams i combine
the new peugeot 307 Hybrid (if it will ever be build) with this batteries ...

and i will save 66% of my momentanean fuel consumption


You could always get a used Prius (warranty already expired or close to it)

Cars.com shows precisely 4 used 2nd Gen Prii in the US with more than 100K miles for sale, starting at $14K. So let's see. $14K for the car, $1,500 to have it shipped to me, then how much is the PHEV conversion? Hymotion won't even put pricing on their website, and the one site I did find that had pricing was outrageous - $24-32K for just the conversion.

Hymotion published fleet pricing (100+ vehicles) at $9,500, so my original estimate of $10-15K for a one-off conversion seems appropriately conservative. Let's take the average ($12,500) as the PHEV conversion cost.

Car - $14K
Taxes and fees - $1K
Shipping - $1.5K
PHEV conversion - $12.5K
Total - $29K

Let's use the Nilar numbers for the battery pack as a baseline for operating costs and lifecycle battery costs.

2,000 cycles
6.4 kWh capacity
20-25 mile range (22.5 mile avg)
$6-7K for the battery pack ($6.5K avg)
12.27 cents/kWh (avg US residential electricity price + taxes and fees)
Energy cycle efficiency of the battery - ~86%

That comes to 4.1 cents per mile for electricity and 14.4 cents per mile for the amortized cost of the battery, for a total of 18.5 cents per mile.

By comparison, a Prius costs 5.9 cents per mile for gasoline and I can get an '08 new Prius for $23K after taxes and fees.

Used car with 100,000+ miles, no warranty, $29K, 12.6 cents more per mile, and even an extra ton of CO2 every 45K miles. Or, a brand new car for $6K less, 12.6 cents less per mile, full warranty, less CO2, and no aftermarket hack that could potentially mess up my car.

Real tough choice there.


jack: I've already agreed that the numbers aren't favourable at $3/gallon gas. Where I live gas is closer to $4 and electricity is 6 cents/kwh and a new Prius is 35K (tends to narrow things somewhat) Don't forget that amortizing the cost of the battery over 2000 cycles is a worst case scenario. Use of the batteries reduces wear and tear on the engine. Any extra carbon from a PHEV only applies if the duty cycle is very unfavourable (and you're running off of a dirty grid, I'm lucky enough to live in an area where the electricity is almost entirely carbon free hydro).

so ... if you're not willing to spend a little extra to encourage the technology, get yourself a brand new Prius, run it on gas until peak oil hits, and do the conversion when the economics reverse (probably about the same time your warranty runs out).

I've heard that the Hymotion conversion will only work on the Gen II Prius. Have you seen anything about this one requiring the Gen II?


I agree there is no question it's not a good time to enter the market for used Prius cars at these price points. And, typically most used Toyota models retain a higher resell value.

I think it's just too early in the game and the demand for HEVs is still high; but, that will change as the other auto companies bring their HEVs to market. Trouble is that could take five to ten years before they hit the used car market place at affordable prices for battery upgrades. Until then, the only low priced Prius' I have found on the market are "rebuildables" from the wrecking yards or flood cars from New Orleans.

Guess I will keep driving the old Volvo for quite a while longer waiting for the BEV and PHEV market to pop.


Where I live gas is closer to $4 and electricity is 6 cents/kwh and a new Prius is 35K

I assume you're in BC.

The highest mileage Gen2 Prius on Autotrader goes for Can$21K. Add at least another Can$1K for taxes and fees, right? So that's Can$22K for the used Prius.

An '07 Prius has an MSRP of Can$31,280. The '08 will go for US$1,200 less for a base model, so with taxes and fees, it's probably around Can$31K for an '08.

Add Can$13K for the conversion.

Used PHEV - Can$35K
New HEV - Can$31K

Put in the Can$4.20/gallon gasoline cost and the BCHydro electricity cost per kWh (~Can$0.088 per kWh with taxes and fees), and you get 2.9 cents per mile for electricity, 15.2 cents per mile for the battery, for a total of 18.1 cents per mile. Gasoline is 8.8 cents per mile.

The only real advantage is not putting 9 tons of CO2 in the atmosphere over the life of the battery (less the CO2 content from making, delivering, and disposing of the battery), since I assume your electricity is all hydro. But economically, it doesn't make sense. It would take 222K miles to pay off the fuel cost difference alone (5.9 cents per mile).


jack: you are essentially correct (any quibble I have over the amortization of the battery would likely only take the payoff distance down to 150K miles using your numbers). A base Prius is $34,888 out the door (toyota.ca). I'd be willing to pay the extra couple of hundred to keep the extra 9 tons of CO2, and other pollutants, out of the air. Not everyone would.

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