It's less than three years for laptop Lithium ion batteries with onboard
charge optimization that are rarely if ever completely discharged,
albeit more deeply discharged than Prius'.
With every charge a lithium cell loses lithium. Typically,
economically-useful versions of such chemistries are limited to
200-300 cycles. The number diminishes rapidly if the circuitry
permits max range between charge and discharge, which is always
the case in laptops because of marketing demands ("Ours runs 5
hours on a charge!"). Nickel-metal-hydride cells are good for
1000 or more cycles, and many more if kept well within those
limits - that mode of operation is practical only when charge
life is unimportant because the "charger" is always connected,
which in this case is the ICE.
Note that the electric motor system on this vehicle is designed
to operate ONLY at that point in the power delivery curve where
the Miller-Cycle engine - required for high mileage - performs
so poorly that it would be unacceptable.
It's a great combination: an electric motor has max torque at
zero RPM, and a Miller (or Atkinson) cycle engine has terrible
low end torque. On the other hand, that wonderful engine design
(an adaptation of the indestructible Echo engine) delivers great
efficiency once the system is moving. And, by unloading the
engine during high-stress initial acceleration, its life is
extended. Supporting that "marriage made in heaven" requires
only a small battery comprised of good quality cells, and it can
be operated in a manner that has a high probability of long life.
Actual numbers tell the story - these systems clearly have a
very low failure rate, and some have been on the road (in Asia)
for more than ten years. Cell technology and management
electronics both continue to improve, so one can reasonably
expect that today's batteries will have an average MTBF even
better than that of the cars built in 1997...
Experimenters with lithium cells in cars are having problems
dealing with the lifetime cycle problem, which will be very
costly despite the performance:weight advantage of that battery
chemistry. There are other chemistries out there with similar
energy densities at lower lifetime cost - don't be surprised if
one of the zinc chemistries leap to the front in the next few years.
My understanding from Toyota is that the NiMH battery was chosen over LiIon
primarily because LiIon batteries have predictable lives and NiMH batteries
do not. Edison cells are a good example of batteries with no predictable
life span. http://en.wikipedia.org/wiki/Edison_cell
Michael Pardee wrote:
It's interesting that the Edison cell has lost favor in the
west, but other nickel+?? technologies continue to emerge, as
well as zinc+??
The cell with the highest energy density of which I'm aware (but
disposable) is for hearing aids - zinc/air. There is one
derivative of that chemistry that might one day become suitable
for rechargeable vehicle use.
Toyota does not specify a battery replacement interval.
They do specify, however, a brake fluid replacement interval.
The OP asked about the replacement interval for the battery. While it
may come to the point where it must be replaced, there is no set
Very dumb, bob, to talk about how the Prius battery has a predictable
life when Toyota and experience both indicate otherwise.