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UC Davis Researchers Suggest the “Battery Problem” Seen to Be Slowing Electric Drive Commercialization Is Perceptual as Well as Technological

Distribution of battery requirements for consumer-selected PHEV designs (shaded circles) compared to USABC, MIT and EPRI performance requirements. Source: Axsen et al. Click to enlarge.

Addressing the widely held notion that battery technology and cost remain as barriers to the initial commercialization of electric-drive passenger vehicles, researchers from the Institute of Transportation Studies at UC Davis are suggesting that part of the “battery problem” is a mismatch between established performance goals and what consumers may initially seek from electric-drive vehicles.

In a paper published in the journal Transport Policy, Jonn Axsen, Ken Kurani and Andrew Burke explore two aspects of the “purported problem” in the context of starting a market for plug-in hybrid vehicles (PHEVs): performance goals, and the abilities of present and near-term battery chemistries to meet those goals.

We contend that potential solutions to the battery problem are not just a matter of technology development and cost reduction, but instead involve a concurrence between battery technology and appropriate PHEV performance goals. The present analysis explores both, with a particular emphasis on the latter—challenging untested assumptions regarding consumer valuation of PHEV capabilities.

—Axsen et al.

Goals set forth by government, industry and academic sources considered in the study include:

  • The US DOE (2007) draft PHEV R&D plan sets a mid-term (2012-2016) goal of commercializing PHEVS with an all electric charge depleting (CD) range of 20 miles (AE-20) and/or a blended charge depleting range of 40 miles (B-40), progressing towards long-term commercialization (2016-2020) of AE 40 or B 60.

  • The USABC specifies two PHEV designs to guide its battery requirements: an AE-10 crossover and AE-40 mid-sized car.

  • MIT proposes a B-30 mid-size car, with a more aggressive driving cycle simulation.

  • EPRI assumes PHEVs to be AE-20 and AE-60 mid-size cars.

Influential PHEV Performance Goals (as summarized by Axsen et al.)
CD Range Miles 10 40 30 20 60
CD operation Type AE AE B AE AE
Body type Type Cross-over SUV Mid-size car Mid-size car Mid-size car Mid-size car
Electricity use
(grid only)
kWh/mile 0.42 0.30 0.19 0.24 0.24
Depth of discharge Percent 70 70 70 80 80
Drive schedule Type UDDS UDDS UDDS, HFWET,
Battery mass kg 60 120 60 159 302
Vehicle mass kg 1950 1600 1350 1664 1782

To explore whether are not those are the right goals for consumers, the research team created a design space in which consumers could create their own designs, and thus set their own PHEV goals. Parameters of the design space included all-electric (AE) or blended (B) operation, and CD ranges of 10, 20 or 40 miles. The design space was presented to a sample of 2,373 new-vehicle buying households in the US.

Our design space approach differs from a common approach to estimating consumer demand for alternative vehicles: eliciting consumer preferences or willingness-to-pay [WTP]. There are several reasons why we implemented the design space approach.

First, we were not willing to assume what a PHEV “should” be. Second, in order to derive consumer-driven battery requirements to compare to experts’s assumption-driven requirements we need consumers complete vehicle designs—it is neither necessary nor sufficient to estimate partial-attribute values or overall WTP.

...Third, constructive design processes are consistent with theories of constructed preferences that view consumer preferences as outcomes of, not inputs to, decision contexts and processes. Willingness-to-pay presumes consumers have preferences about the attributes available in a given choice. However, research suggests that most consumers have little experience or understanding of electric drive, and have difficulty quantifying their valuation of fuel economy.

—Axsen et al.

The analysis simplified the results into two categories: cars and trucks. The majority of the potential early market respondents (69%) selected the based B-10 design—i.e., the PHEV design with the lowest battery power and energy requirements. Using the results of the design study (and using only the more aggressive US06 cycle) the team assessed the resulting battery requirements for power, energy, longevity, cost and safety.

They found that the requirements derived from prospective consumers are within the capabilities of several lithium-based battery chemistries, and even that some NiMH batteries can meet energy density, ir not peak power density, requirements of most PHEV designs created by new car-buying households interested in PHEVs. They note that other requirements may make NiMH unsuitable for PHEV applications.

However, the research reported here indicates that more important than concerns about technology development per se is the perceived problem: the previously untested assumptions regarding the types of PHEVs to be commercialized. contrast to statements by battery researchers indicating that accelerated PHEV development may be a misguided “detour” due to the large gap between present battery performance and performance requirements for PHEVs, we are saying that appropriate batteries may be closed for commercially viable PHEVs than often realized and that the battery problems to be solved for those batteries are radically different from the power/energy/life/cost/safety issues implied by the USABC and others.

—Axsen et al.

These findings have significant implications for policymakers, Axsen et al. say. For example, the individual federal tax incentive of $2,500 to $7,500 for the purchase of an electric-drive vehicle only applies to vehicles with a battery pack larger than 4.0 kWh in capacity.

The 4.0 kWh lower limit on battery size is difficult to reconcile with the fact that of the people in this study who designed a PHEV for themselves in the high cost design game, over 90 percent designed a PHEV that requires a battery smaller than 4.0 kWh and nearly 75% designed a PHEV that requires a battery smaller than 2 kWh.

—Axsen et al.


  • Jonn Axsen, Kenneth S. Kurani, Andrew Burke (2010) Are batteries ready for plug-in hybrid buyers? Transport Policy 17 173–182 doi: 10.1016/j.tranpol.2010.01.004



While their methodology sounds like it has obvious flaws (people say they want one thing, but actually buy something else), they do raise an interesting point.

Why is it that our choices are a Prius's tiny little electric motor that can get you up to neighborhood speeds before hte IS kicks in or a Volt's highway capable complete electric drivetrain with generator backup?

It seems like there is space between these options for a 30-45mph-capable for 10-15 miles parallel hybrid.


Future higher performance lower cost battery technologies are still being developed in 50+ labs and start ups around the country and another 100+ places around the world. Nothing worthwhile may hit the market place much before 2015/2020 unless industrial nations invest much more aggressively in R & D and large mass production automated facilities.

Meanwhile, various electrified vehicle configurations will be offered as gap fillers, HEVs, with small batteries, will be around for another 5 to 10 years and PHEVs, with various e-range and size, will be around for at least 20 years.

Short e-range city type BEVs will co-exist with the other two for many years. Long range, light weight, BEVs with improved performance and lower cost batteries may not be available (at an affordable price) much before 2020 unless somebody comes out with a major battery technology breakthrough in the next two or three years.

Two decades to go from inefficient polluting ICE vehicles to high efficiency clean electrified vehicles is not that long.


@Harvey going "from inefficient polluting ICE vehicles to high efficiency clean electrified vehicles" is a green fallacy. The reality of is BEV's go from one GHG source, the ICE, to another, the grid, that is probably less efficient overall. The recent posts about fast charging stations to support BEV's illustrate the fallacy. Fast charging will force the grid to add peak capacity, likely sourced from nat gas turbines. Fueling the vehicle directly with nat gas would make more sense and generate less GHG.


"over 90 percent designed a PHEV that requires a battery smaller than 4.0 kWh and nearly 75% designed a PHEV that requires a battery smaller than 2 kWh."

Sure, most said under 2 kWh until they find out that it has short range. Is it even worth it to plug in less than 2 kWh?
One kWh can be charged in less that an hour and take you about 4 miles, so I do not see the advantage.


The advantage is that the battery power can be used for low speed driving and city use.
If you live in Nebraska, forget it, if you live in Seattle or Boston, it might be for you.

The biggest gains are to be made with a small battery - as you increase the battery size, the fuel economy improves less for each KWh added.

You are better off with 100K 2 KW hour PHEVs than 50K 4KWh PHevs.

So I agree with their point that the threshold for the PHEV rebate be lowered from 4 to 2 KWh.

+ lots of people make short journeys and could do the whole lot in 2KWh (or 1/2 of it for battery lifetime reasons).

Perhaps what you need is a car which can literally plug itself in every time you return it to your garage or driveway. Thus, it would always be fully charged (though perhaps not at night rates when power is cheaper).
[ You could add a smart charger as well .... ]


nordic: I have no particular argument with NG vehicles, they are certainly an improvement on gasoline or diesel vehicles, but I'm afraid the rest of your post is an echo of petroleum industry shill lies.
1) The "long tailpipe" talking point has been demonstrated many times to be a worst case scenario. Using numbers from Argonne NL a CNG ICE vehicle will use arround 4,500 btu's per mile (releasing about 300gCO2/mile). An EV from the US grid (which nowhere near as clean as the Canadian grid) will use just about 2,500 btu's per mile (less than 250gCO2/mile). These numbers are well-to-wheel. Electrical generation from NG (combined cycle) is much more efficient than ICE engines. (both electricity and NG have transmission losses/expenses, electric motors are very efficient but not perfect, NG requires energy to compress it for transport in a vehicle)
2) "The grid will collapse" .. another scare tactic for a worst case scenario. The best case scenario requires no new infrastructure and makes much better use of existing generating facilities. Personally, I charge at night and start the next day with a full "tank".


Nordic: Neil is correct, EVs emissions are lower, even when grid-powered, and that advantage will grow with time, as the grid gets cleaner. I charge my car at night, and I don't mind the slow speed of charging. Fast charging will be best done in conjunction with smart metering and charging systems that can tell when the power is cheapest and most available. Detering people from peak time charging can be done with a properly-designed incentive system. The $300 billion or so that goes out of the coutry per year for foreign oil is a huge opportunity to create a domestic industry to power cars. Vehicle electrification will have huge benfits enconomically and environmentally.



Our electricity is currently 98% Hydro + 2% Wind. As more and more wind turbines and Hydro plants are being added, the ratio may slowly change but it will remain at 90+% Hydro for decades to come.

Other countries (like France) are 80% Nuclear. Not all countries rely on lower cost dirty coal fired power plants. Even USA is progressively switching to cleaner Nuclear, NG, Wind and Solar energy sources.

With solar panels efficiency going up (above 21% now and 30+% by 2020) and cost per watt going down, many residences will install PVs to generate a high percentage of the e-energy they use. The equivalent to 6 to 10 Kwh required daily by the family BEV or PHEV could be produced with a 2 KW installation. The surplus could be used by the family house or sold to the main e-power supplier.

E-energy does not have to be from polluting sources.



China just started a massive national program to promote the use of solar panels on all residences and buildings by 2020.

Sales of higher efficiency solar panels (in Asia, Australia, Africa, southern Europe and southern USA) will multiply during the next 10 years. Another positive secondary effect will be reduced demand on the distribution power grid. Eventually, energy efficient homes equipped with enough solar panels, large storage batteries (ex-vehicular units) and V2G connexions could become net clean e-power suppliers.


I would like enough solar panels to power my car and home. When they get down to about $3 per watt installed, that may be possible.



You may have to wait another 5 years or so and do some of the installation work yourself but it will come, specially with future technologies such as printed roll to roll panels. Storing the energy for non-productive periods may be more expensive, at least for the next 10+ years.


Nanosolar is selling to utilities right now, but they may start selling to end users. If it is like Unisolar, they will sell at market rates to make money for expansion. I am waiting for some company to just make an all out effort to reduce the price, but when they can sell all they can make at present prices, that is what they will do.


"The $300 billion or so that goes out of the coutry per year for foreign oil is a huge opportunity to create a domestic industry to power cars. Vehicle electrification will have huge benfits enconomically and environmentally."

More like $450B in 2008. Yes. That money is on the table for the taking by domestic industries that can find viable alternatives to oil. As vexing as it may be to the global government dream - our best hope for fast transition to lower carbon energy is national energy security and the jobs it will create. Clean grid energy is near term resource for EV charging. Later, distributed residential power units combining solar and CHP will generate clean energy locally and dispense with high voltage grid wiring.


"The $300 billion or so that goes out of the coutry per year for foreign oil is a huge opportunity to create a domestic industry to power cars. Vehicle electrification will have huge benfits enconomically and environmentally."

More like $450B in 2008. Yes. That money is on the table for the taking by domestic industries that can find viable alternatives to oil. As vexing as it may be to the global government dream - our best hope for fast transition to lower carbon energy is national energy security and the jobs it will create. Clean grid energy is near term resource for EV charging. Later, distributed residential power units combining solar and CHP will generate clean energy locally and dispense with high voltage grid wiring.

John L.

I agree with the general conclusion made by the UC Davis researchers. I don't think that the short-term PHEV goals advanced by various agencies and interests are sufficiently modest. The GM Volt is overkill, and it appears that its price will reflect that fact. They are making the perfect the enemy of the good. Sometimes I wonder if it's intentional -- just like those people who say "the wind doesn't always blow, and the sun doesn't always shine" as an argument against expanding renewable energy.

Anyway, I bought my Prius in 2004, and my home solar PV system in 2005. I would really like to do a little driving on sunshine, so to speak. (I'm grid-tied, so technically the electrons I use for driving might not be "my" electrons -- but you get the idea, I hope.)

I've stated a number of times on this forum that I would buy the NiMH-based, PHEV-7 Prius that Toyota has already demonstrated, for a $2,500 incremental cost. I would buy this today if I could get it. That's very much on the low side of the agency targets.

Plug-In Solutions (I'm not affiliated with them in any way) offers a 20-mile blended-mode Prius conversion using a 4 kWh, LiFePO4 battery. You don't have to modify the car's suspension, and you still have a spare tire.

Plug-In Solutions charges $7,000 for that upgrade. That's a bit rich for me, but not by much. Getting it down to $5,000 would put it in the "buy it now" category for me, assuming that I can take that "life of vehicle" promise about the battery at face value.


Henry Gibson

The EFFPOWER lead acid bipolar design or the Csiro lead acid ultra-capacitor design batteries are well suited for the high powers needed for acceleration from stops. Small flywheels such as the electric version of the Flybrid technology can also be used in electric vehicles for high acceleration. Some version of the Firefly carbon foam technology is more than sufficient for a cheap battery for a 20 mile range as has been demonstrated by Ron Gremban of Calcars with his first version of the Prius+. Calcars and ACpropulsion and Ian Wright have all demonstrated that a PHEV can get five miles or more on a kilowatt hour, except for Ian Wright, they have also all demonstrated this with lead acid batteries that are relatively cheap. Some versions of pure lead grid spiralwound absorbed glass mat batteries demonstrate a possibility of having a long cheap life as well; compared to NiMH. Bipolar nickel cadmium batteries are also suited very high acceleration power and long life.

What people want and what they will use for transportation, if necesssary, are almost exclusive. The Tesla is the ELECTRIC HUMMER and was designed for high cost and high electric consumption, but this is disguised by the fact that electric motors have a high efficiency at low and high speeds and when the vehicle is stopped at a light, sign or in traffic. Introducing 50 mph speed limits on motorways within cities and near them would cut massive amounts off of fuel use. No high speed car can be considered energy efficient. I do not mind people operating cars at high speed as long as they are not pretending to be ecologically correct just because they have a TESLA.

A limited speed plug-in-hybrid electric car designed for the lowest possible cost similar to the TATA NANO is the way to get electric cars on the road. It is bad engineering to eliminate internal combustion engines from electric cars. It may also be bad engineering to use expensive transistor converter boxes to run the car's electric motors. Motors with brushes and speed control resistor switches are adequate for almost every electric car use, but eventually the price of electronics of car motor control can get low as the price for computer memory did.

Atomobiles that are used usually only for short distances should not have an expensive hundred mile battery in them.

I case anybody has forgotten, a standard ZEBRA battery pack has been able to move a Prius+ 80 miles for over ten years. The cost could be much lower if millions were made.

Liquid fuels can be made from nuclear or solar energy at a cost much lower than 150 a barrel and use recycled CO2 as well, so there is limited reason for long range total electric vehicles. Recent fuel cell developments do not induce the use of fuelcells in cars as much as that they should be used in combined cycle mode in homes for higher efficiency whilst charging batteries. The small fuel cells are an option instead of range extending engines but are too expensive. The OORJA methanol one should be installed in TH!NKs and TESLAs since their price is so high anyway.

Lead batteries do not need to last the life of the vehicle because their cost is so low and the cost of energy stored in them is acceptably low. ..HG..

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