[Focault's Pendulum]

These lithium batteries experience a gradual drift into senescence as they age. That is, they develop an increasing internal resistance that reduces their charging capacity. No one know how long they will last before they need to be replaced. Cost estimates are between $9,000 and $18,000 to replace

What no one is revealing is that any rechargeable battery has a memory.

Example:
If you constantly charge your cell phone while it has a half charge on it, And this does take a while) when it eventually runs all the way down, when you charge it to full, it will only have taken a half charge.

[jonrick46]

The nickel cadmium (NiCd) battery has memory effect, but the nickel metal hydride (NiMH) battery, used in such things as cordless drills, does not suffer from this effect. The lithium-ion (Li-Ion) battery also does not suffer from the memory effect. It does suffer from the effects of age. Many manufacturers remain silent about this issue. After one year, whether these batteries are used or not, they will suffer a deterioration in capacity due to the development of internal resistance due to the chemical composition of the battery.