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Green Auto News: Mr. Green Car: State of charge: Hybrid and electric car batteries
By Allen Penticoff
More and more vehicles are becoming dependent on batteries to boost their fuel economy. This will drive up costs, not only for the batteries themselves, but the electronics to control them and the electric motors that provide the mechanical force to transmit the stored electrical energy.
Now that about 3 million Toyota Priuses are on the road, people are thinking more about what it may cost to replace the drive battery pack. First, there are two batteries in the Prius, as there are in most other hybrids. One is a standard lead-acid 12-volt battery like that found in any other car. This powers all systems that are unrelated to the drive motor. You can replace this yourself for $200 or less. It will last about as long as most regular batteries. The other is the traction battery pack (in a Prius), which is a large Nickel Metal Hydride (NiMH) battery that Toyota presently lists for $2,588. Online forums indicate the whole cost, including labor, is about $3,700 — although a few brave souls have found batteries for less cost and replaced it themselves.
When will that battery need to be replaced? When performance drops off noticeably. Like all batteries, they lose storage capacity over time. The warranties on most hybrid and electric cars are eight years and 100,000 miles for the traction battery pack, though if you live in California, that is 10 years and 150,000 miles. There are many reports of early Priuses going 200,000-300,000 miles without replacing the traction battery. One story of a man driving six hours a day commuting (yikes) had put 500,000 miles on his Prius without doing anything to the engine or replacing the battery. However, online forums are indicating most are living about 150,000 miles before replacement — and some owners are irate at the cost, while others anticipated the cost from the day of purchase and have written off the cost as part of ownership of an efficient vehicle.
While the Prius has a NiMH battery (mostly for long life), most makers of electric vehicles (EV) are relying on Lithium-Ion (L-ion) batteries to provide electrical storage. Lithium itself is a fairly common element on Earth, and mining is not very expensive. But L-ion batteries are each full of fancy, delicate architecture and controlling electronics — thus driving up the price. The nature of these batteries allows a cell voltage of 3-4.2 volts that must strictly stay within those limits to avoid explosion from overcharging, or failure from low voltage. In an EV, there are hundreds of these cells linked together in a series to obtain a voltage high enough to be usable in the powerful drive motors.
You may see Lithium-Iron batteries advertised now. At first, I thought it was a misspelling. But it is correct, the latest in Lithium-ion battery technology uses a lithium iron phosphate cathode that yields a bit less energy density in favor of a far more stable (and safer) cell. I’ll still refer to them as L-ion here. L-ion batteries have some great advantages. Not only do they not have a “memory,” but they thrive on frequent small charges — although they are able to take a very fast charge, too. A sure way to kill a L-ion battery is to let it sit around until it slowly self discharges completely. Internal circuitry will not allow the cell to be recharged once it gets below 3 volts — so it is effectively dead. They don’t particularly like high heat, either, which could lead to decreased performance and even explosions. But don’t worry, your EV and hybrid car batteries have been tested in all conditions you are likely to encounter without a failure.
On the horizon are new “solid state” L-ion batteries. These are in development to eliminate much of the complex structure and chemistry in these batteries. The solid state batteries may be three times as energy dense while costing only half as much as present batteries. There is a cost hurdle right now in how the controlling electronics are fabricated. But as important as batteries are to transportation now, I expect a resolution soon.
Replacing the traction battery in a Nissan Leaf or Chevy Volt will be very pricey. The bigger the battery — the more cells that are needed — the greater the cost. While I’ll still promote driving EVs, one should start a savings plan for the day the battery needs to be replaced — then it won’t be such a shock. I think the cost per mile with charging cost and battery replacement factored in will still be money ahead of driving purely on gasoline or combinations thereof (hybrid).
The conversion to electric driving is happening — I’ve encountered my first Leaf being driven on the highway now. Only a matter of time, and there will be thousands of them once Nissan begins building them in their new plant in Tennessee.
From the Feb. 22-28, 2012, issue