~ How it works
~ the Tesla Roadster is powered by Lithium ion (Li-ion) batteries
~ Energy Storage System is comprised of 6,831 individual Li-ion cells
~ it’s roughly the size of a storage trunk and weighs about 900 pounds
~ nestled securely in the back of the Tesla Roadster
~ the battery system is the secret behind 0-60 mph acceleration and phenomenal driving range
~ the Li-ion battery system represents the very best of today’s commercially available battery technology
~ Li-ion batteries are a whole lot better than Nickel-Metal Hydride (NiMH) cells and lead acid cells
~ there is still a tradeoff between energy and life, even within the family of Li-ion
~ all batteries age, and they lose capacity as they do, which in turn, shortens driving range
~ batteries age with use, and they age with time, even if not used
~ two kinds of aging: aging from use, called “cycle life,” and aging with time, known as “calendar life”
~ these two different aging mechanisms can be thought of as separate, overlapping forces
~ environmental conditions such as temperature and humidity affect each aging mechanism in its own way

Cycle Life
~ the number of full discharge-charge cycles that it takes to reduce a cell’s capacity to some fraction of its original state
~ a common threshold used in the laptop industry is 80 percent
~ note that the cell is generally not completely dead at the end of these cycles
~ it has a significant number of useful cycles left, just at a lower capacity.
~ not all cells are created equal
~ avoiding very high and very low states of charge
~ voltages over 4.15V/cell (about 95 percent state of charge [SOC]) and voltages below 3.00V/cell (about 2 percent SOC) cause more stress on the insides of the cell (both physical and electrical)
~ charging faster than about C/2 (two hour charge) can reduce the cell’s life
~ avoide charging at temperatures below 0° C (Tesla's design heats the pack before charging at cold temperatures.)
~ avoide very high discharge rates (Tesla's pack has been designed such that even at maximum discharge rate, the current required from each cell is not excessive)
~ 6,831 of these little guys power one battery pack
~ there is a huge difference in cycle life between a 4.2V/cell charge (defined by the manufacturers as “fully charged”) and a 4.15V/cell charge
~ 4.15 volts represents a charge of about 95 percent
~ for this reduction of initial capacity (5 percent), the batteries last a whole lot longer
~ unfortunately, further reduction of charge has a much smaller benefit on cycle life
~ Tesla Motors has decided to limit the maximum charge of its cells to 4.15 volts, taking an initial 5 percent range hit to maximize lifetime of the pack
~ Tesla also limits discharge of the battery pack to 3.0V/cell and will shut down the car when the batteries reach this level
~ limiting the charge rate is less of a compromise, since the wire size and availability of very high current outlets
~ limit much more than the batteries do at this point

Calendar Life
~ Li-ion cells lose capacity with time, even if they are just sitting on a shelf
~ they lose the most early in their life (year one) and then continue to lose capacity gradually thereafter
~ two factors shorten calendar life considerably:
~ lifetime average temperature and time spent at high states of charge
~ batteries would last the longest if they were stored in a refrigerator at a very low state of charge
~ they age the fastest when stored in a hot place at a full state of charge
~ – like those in your laptop computer, plugged into its charger and being cooked by a toasty Pentium processor

~ at Tesla Motors one of the key inventions to maximize battery lifetime is
~ a sophisticated liquid cooling system that maintains a favorable temperature for the batteries,
~ even under extreme ambient conditions
~ the cooling system engages to try and keep the temperature of the cells below 35° C at all times
~ and the lifetime average temperature at or below 25° C.

~ the other significant factor that affects calendar aging is the charge state of the battery during storage
~ at higher charge states cells lose capacity faster
~ this is a second reason Tesla has limited the maximum state of charge to 4.15V/cell instead of 4.2V/cell
~ Tesla also offers the driver the option of charging to only 3.8V/cell (~50 percent) or
~ 4.10V/cell (~90 percent) to further extend calendar life if the full vehicle range is not needed on the next few trips
~ Tesla advises and encourages a full (4.15V/cell) charge only when it is needed

So what does this all mean for the real-world performance of a car?
~ as batteries in any EV age, they lose capacity and the vehicle will lose range
~ this is unavoidable and true in any EV with any type of battery
~ you can think of this as a very slow reduction in the volume of your vehicle’s “gas tank” over its lifetime
~ Tesla limits how fast this aging and loss of range happens by
~ selecting the best cells, designing the best cooling systems, and carefully managing charge states
~ Tesla expects more than 100,000 miles of driving range and more than five years of useful life
~ at the end of this period the pack will have less capacity than when new
~ (just like an internal combustion engine has less power and much worse emissions than when new
~ If, for example, you drive 10,000 miles per year at the end of five years you will have around 70 percent of the energy storage capacity of when new one

catch ~>Content @Electric Cars!