The working principle and composition principle of an action power supply is simple. In situations where an external power supply can be found, the built-in battery is pre charged, which inputs electrical energy and stores it in the form of chemical energy. When needed, the battery provides energy and generates electrical energy to reach the required voltage through a voltage converter (DC to DC converter), The output terminal (usually a USB interface) supplies power to the required device for charging or other purposes. The basic composition of an action power supply has three basic functions, including energy storage, charging, and power supply. Other functions such as safety protection, battery status detection, and display are added according to the needs of different designs, purposes, and convenient operation. Energy storage (batteries) In order to provide power to other devices without external power supply, the mobile power supply requires batteries as energy storage. Most mobile power supplies use lithium-ion batteries (Li ion) or lithium-ion polymer batteries (Li PO), with a small portion using nickel hydrogen batteries (Ni MH), and some early mobile power supplies also used a single battery. Lithium ion batteries (Li ion) or lithium-ion polymer batteries (Li PO) have the highest energy density, i.e. the lightest and thinnest, whether measured by weight or volume. In addition, lithium-ion/ion polymer batteries have higher efficiency during charging and discharging (less energy/electricity wasted). But the price is also the highest among these batteries, and overcharging or discharging can easily cause permanent damage to the battery, so more precise electronic circuits are needed to control charging and discharging. Due to the spontaneous combustion of lithium-ion/ion polymer batteries at high temperatures, safety and stability have become extremely important requirements, and reliable safety protection circuits are needed to prevent any situation that may cause overheating. Lithium ion batteries have a hard shell, while lithium-ion polymer batteries do not. Therefore, in theory, lithium-ion batteries will be slightly heavier. However, lithium-ion polymer batteries do not have a hard shell, making it easy to make specific sizes to match their appearance. However, lithium-ion polymer batteries will expand slightly in size after being fully charged, and space needs to be reserved during design to avoid danger caused by excessive pressure inside the battery&Nbsp; Performance measurement: Power supply efficiency: During voltage conversion and charging of mobile power sources, there is a loss of electrical energy. The less the loss, the better the performance. Safety protection: overcharging protection: to prevent overcharging of the battery. Overvoltage protection: prevents the battery charging voltage from being too high. Overdischarge protection: prevent excessive battery discharge. Overload protection: prevents continued discharge in the event of high output current. Short circuit protection: prevents power supply from stopping due to short circuit detection at the output end. Overheat protection: prevent excessive temperature. Stability of voltage and current. The quality of the battery cell&Nbsp