Testing or replacing the cell isn't the problem, once the pack itself is exposed. It's the labor involved getting to it. If the packs are unitized in some way, or are housed in a common assmembly, it takes X number of hours to be able to acces some or all of the pack. If you do it once for every cell then the overall cost of replacement is labor times the total number of cells plus the battery price. Even figuring in a mere hour labor for each cell, the labor costs could easily run into the thousands of dollars. I'll pick an arbitrary value of 100 volts DC. That's 50 cells, roughly. At one hour each and a shop rate of $75 per hour, that's $3750 ... roughly the cost of the replacement pack. If the entire pack took TEN hours to replace at $75 per shop hour, that's still a savings of $3000 over the life of the vehicle. And that's not counting the fact that single cells will likely be 20-50% more expensive per cell than a complete pack.
If it takes an hour per cell they designed the pack wrong. Call it an hour to pull the battery out of the car and put it or a replacement back in, an hour to access the cells in the pack, then an hour to test ALL the cells. It shouldn't take anywhere near an hour to test an individual cell. All you need is a voltmeter for most types, starting from a charged pack. If you want to be more complicated, there are more thorough testers, but they should all be fast. Or if not, be able to test an entire battery pack at once.
A good analogy would be the lifters in a small block Chevy. Replacing the lifter is no big deal once you get to it, and the part is relatively inexpensive.
Or it could be like spark plugs, where it's not really difficult at all. Most battery packs are located under the trunk/passanger seat, it shouldn't be that difficult to get to it.
Not by much. Run the numbers and the "break even" it's still much longer than most of us will ever own a vehicle.
Remember that most hybrids get better city mileage than highway mileage, normally get a few more mpg highway than a non-hybrid, and a LOT more city.
Thus, an inner-city cab pits the best parts of a hybrid up against the worst parts of a traditional gas vehicle, plus puts enough miles on quickly enough to overcome the cost of capital and time dedregation of the batteries. It helped that we were looking at car hybrids where the price difference was ~$3k, not ~$10k.
Still - ford's site lists combined mileage as 23 for the standard and 32 for the hybrid. Slightly different than Nick's numbers, but we know about realworld and EPA estimates. Still, I'll go with them because that's what I have. I WILL use Nick's price difference, though Ford only has the 'Comparably Equipped Price' at $5k price difference($4k base). Right now I figure they're discounting the standard types while they can still charge MSRP on the hybrids.
Eh - let's check different numbers.
$4k Base price - 1000 gallons, EPA estimate
(X / 23) - (X / 32) = 1000, 81.8k miles to break even
'Cabbie' - $5k difference, 1250 gallons, 20mpg vs 34 mpg(100% city)
(X / 20) - (x / 34) = 1250, 60.7k break even.
I have to go now, I might post some more estimates when I get back.