Antennas, Base and Mobile Stations -13.Battery
Another important factor in developing compact and lightweight mobile and portable units is to increase the energy density in proportion to the volume and weight of the battery. Battery types include both disposable primary batteries such as ordinary dry cells, and secondary batteries that can be reused after recharging. Portable units use secondary batteries that can be reused after recharging, such as Ni-Cd batteries, nickel-hydrogen batteries and lithium-ion batteries.
The energy density of various batteries has been steadily improved. In particular, the lithium-ion secondary batteries that have rapidly been adopted for more and more applications in recent years have an operating voltage of some three times that of Ni-Cd or nickel-hydrogen batteries, with both a per-volume and per-weight energy density that is considerably higher than past products. In sum, we expect that lithium-ion batteries will see even greater usage in the future because they produce a high-energy output despite being compact and lightweight.
Improvement in the Energy Density of Small Secondary Batteries