Why Low Power?
Slide 3 of 30
Sony introduced the rechargeable Lithium-ion battery in 1991 as a better alternative to Nickel-Cadmium rechargeable batteries. They did not really catch on until the mid-1990's, however, because of the high price. Price is no longer the issue, with Li-Ion batteries costing approximately 10-15% more than alternatives today.
Li-ion features a factor of 1.5 improvement in charge/volume ratio, and nearly a factor of 4 improvement in charge/mass over the older Nickel-Cadmium rechargeable batteries.
However, battery progress is painfully slow: no new promising technologies have been discovered that hope to significantly improve over current battery designs. The only major progress since the early 1990s has been the idea of a "smart" battery that will let you know the amount of charge left before you must power down. Not to downplay the importance of knowing the amount of charge left on your battery; it's just that it may improve your efficient USE of the battery, but the battery itself is no different.
Contrast with this the progress of semiconductor (read: processor) technology: since 1990
