EVs’ staying power: Battery cell life proves resilient
BY DAN CARNEY Motor Matters March 1, 2012 2:16PM
The skeptic’s criticism of electric vehicles goes something like this: “Yeah, it gets good mileage, but good luck when the battery goes dead!” It is all part of the process of consumers acclimating to something new.
Ford has been gathering reliability data on its hybrid vehicles, including 80 million miles by hybrid Escapes serving taxi duty — and the news is reassuring. Of the 43 million battery cells installed in Ford hybrids, so far five battery cells have failed.
“Ford’s battery technology is so strong, the odds of experiencing an issue with one of our hybrid battery cells is around 8.5 million to 1 — about the same odds as a person being struck by lightning twice,” said Chuck Gray, chief engineer, global core engineering, hybrid and electric vehicles. “Ford understands that for new technology, reliability can be a concern for customers, so we work extra hard to deliver a trouble-free product.”
This is good, because the battery pack in an EV is costly. Naturally, nobody would want to be on the hook for its replacement. But EV battery packs are composed of many individual battery cells, which are monitored, diagnosed and if needed, replaced, individually.
That is significant because if you are one of the unfortunates whose car suffers failure of a cell — the equivalent of being struck by lightning twice — it still doesn’t mean that you are stranded with a dead car. It means that the computer watching over the battery pack has noticed that one of the cells isn’t pulling its weight, and that its attempts to coax it back into line with various conditioning procedures. If that doesn’t work the driver gets an alert that the battery needs service, and with a visit to the dealer the offending cell is replaced, bringing the battery back to full power.
The first-generation technology Ford Escape hybrid had 250 nickel-metal-hydride cells in its battery, so failure of a cell would have cost it 0.4 percent of its power capacity. So much for getting stranded.
The newer Fusion hybrid has only 208 cells in its nickel-metal-hydride pack. But, the powerful lithium-ion pack in the upcoming Focus hybrid will have 400 cells providing its 23 kilowatt-hour capacity.
On the matter of the expense of replacing the battery pack or one of its cells, hybrid car shoppers should remember that vehicles like the Fusion hybrid have an eight-year/100,000-mile warranty on their electric drive components, so it would be a while before an owner would have to pay for any such repairs.
The battery is only half of the electric vehicle equation, though admittedly the more problematic half. The other half is the electric motor. Ford has installed nearly 190,000 electric motors in cars so far. That’s a much smaller number than the 43 million battery cells, but the failure rate of those motors has been even more impressive: zero. Even our comfortably familiar internal combustion engine can’t match that (non-) failure rate after a century of refinement.
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