Reply #2: Toyota says not a single one has needed replacement [View All]

[LSK]

Helped by rising fuel costs, sales of the second-generation Prius took off. Toyota built about 52,000 of the first-generation cars, and so far has added more than 214,000 of the latest version. That means there have been well over a quarter-million Prius Hybrids sold in the U.S., making it by far the country's most popular hybrid.

And Toyota claims that not one has required a battery replacement due to malfunction or "wearing out." The only replacement batteries sold--at the retail price of $3000--have been for cars that were involved in accidents. Toyota further claims that the nickel-metal hydride (NiMH) battery packs used in all Prius models are expected to last the life of the car with very little to no degradation in power capability.

For those of us who have cell phones and other devices with NiMH batteries, that claim may sound unrealistic. Over time, the battery's charge longevity seems to wane, resulting in shorter and shorter usage between charges. Eventually, the battery becomes worthless and we buy a replacement.

But in the case of most electronic devices, the batteries tend to get fully charged, then nearly fully discharged before being charged again. For the power pack in the Prius, at least, Toyota says this would greatly shorten the life span of the battery.

To get maximum life out of the Prius battery pack, the car's computer brain does not allow the battery to fully charge or discharge. Toyota says that for the best service life, the Prius battery likes to be kept at about a 60 percent charge. In normal operation, the system usually lets the charge level vary only 10-15 percentage points. Therefore, the battery is rarely more than 75 percent charged, or less than 45 percent charged.

http://consumerguideauto.howstuffworks.com/hybrid-batteries-none-the-worse-for-wear-cga.htm