Batteries

Typically, a lithium-ion (Li-ion) battery is the standard form of power in mobile devices due to its energy density. In such a battery, lithium-ions physically move from the negative electrode to the positive. During recharge, the ions move back to the negative region. This is known as an ionic movement.

Batteries also develop memories with many charge-discharge cycles. This capacity loss is expressed as a measure of the initial capacity (for example, 30% loss after 1,000 cycles). This degradation is almost directly correlated to environmental temperature, and loss will increase in a high-temperature environment. Therefore, it is imperative that the architects manage thermals in a constrained environment if lithium-ion is to be used.

Another factor in battery life is self-discharge. When unwanted chemical reactions occur in a battery cell, energy will be lost. The rate of loss depends on chemistry and temperature. Typically, a Li-ion can last for 10 years (at ~2% loss per month), while an alkaline battery will only last 5 years (15% to 20% loss per month).