It may be the second question everyone asks about buying a hybrid: Will the battery pack last the life of the car? (Fuel economy is always first. Always.) So Toyota, Ford, and other patiently note that their packs carry warranties of 8 years / 100,000 miles or 10 years / 150,000 miles, depending where they're sold.

Now comes more proof that the packs hold up to whatever drivers can dish out. San Francisco is retiring its first 15 Ford Escape Hybrid taxis after some of them have racked up more than 300,000 trouble-free miles. They were launched in February 2005, with great fanfare, by mayor Gavin Newsom, split between San Francisco Yellow Cab and Luxor Cab.

San Francisco now counts 1,438 cabs, of which 14% are hybrids. New York's fleet, almost 10 times as large at 13,237, is roughly the same, at 15%. The NYC Taxi and Limousine Commission has just revised its hybrid incentive plan, being fought tooth-and-nail by the taxi owners' group.

Taxis, in fact, may be the best and largest real-world test for hybrids in fleet usage. While several cities are bringing hybrids into their police fleets, taxis in two-shift operation put on more miles and see a wider range of road conditions.  They're also likely to be run far longer than patrol cars, which are usually retired at or before 100,000 miles.

The Escape Hybrid is popular in San Francisco and New York, but it's hardly the only hybrid taxi contender. In fact, Toyota Prius taxis can be seen domestically in Denver, Chicago, Phoenix, Las Vegas, and San Antonio. Elsewhere, they're happily covering ground in Berlin, Ljubljana, Tokyo, and many other cities in Japan.

Prius Yellow Cab in Denver St. Patricks Day Parade

Prius Yellow Cab in Denver St. Patricks Day Parade

[SOURCE: Los Angeles Times; PHOTO: SF taxi by Flickr user Ian Fuller]