The battery used in mobile devices is a masterpiece of chemical engineering. It can store a large amount of electricity in a small block, allowing mobile devices to run for several hours. Most modern mobile devices use lithium batteries, which are composed of two parts: a pair of electrodes and an electrolyte that exists between them. There are many materials that can be used for the electrodes, such as lithium, graphite, or nanowires, but all of them rely on lithium as a chemical component.

Lithium is a reactive metal, so it is easy to synthesize with other elements. Pure lithium is highly reactive and can even spontaneously combust in air, so most batteries use the safer lithium cobalt oxide. The electrolyte between the two electrodes is typically a liquid organic solvent that allows electrons to flow. When a lithium battery is charged, lithium cobalt oxide molecules can capture electrons, which are then released during the battery's use, thereby supporting the operation of mobile phones.

Lithium batteries are the most common type of battery because they can store the most electricity in the smallest space. This is measured by energy density, which is the amount of electricity that can be stored per kilogram of battery, measured in watt-hours (Wh). The energy density of lithium batteries is generally between 150 and 250 Wh/kg, while nickel-metal hydride batteries are only 100 Wh/kg. In other words, lithium batteries are smaller and lighter than other types of batteries, so they can compress the volume of devices while still maintaining a long battery life.

The unit of battery capacity is milliampere-hours (mAh), which represents the overall amount of electricity that a battery can provide. For example, if a battery has a capacity of 1000 mAh, it can supply 1000 mA of current continuously for 1 hour. If your device has a current of 500 mA, then the battery life of this battery is about 2 hours.

However, the battery life of a device is more complex because the specific power consumption of a particular device depends on the tasks it performs. If the screen of the device is on, wireless transmission is enabled, and the processor is running at full speed, it will consume more power than when the screen is off, wireless transmission is off, and the processor is idle.

Therefore, consumers should be more cautious about the battery life claimed by manufacturers-they may extend the battery life by reducing the screen brightness or turning off some components. If you are curious, you can use some dedicated applications to monitor the power consumption and battery status of mobile devices. BatteryMonitorWidget in Android and BaterryLifePro in iOS can both achieve this.

Because of the risk of fire, lithium batteries must be tightly controlled. Battery manufacturers use charging controllers to manage current to achieve this goal. In fact, every battery has a small computer built into it to prevent over-discharge. This component can also control the current entering the battery during charging, slowing down the current when it is about to be fully charged to avoid overcharging. More battery manufacturers now include PTC thermistors in the battery circuit. The PTC thermistor is actually a self-resetting fuse that provides overcurrent protection, making the battery safer.