Charging is an important step in using a rechargeable battery. Appropriate and reasonable charging is very beneficial to prolong battery life, and brutal and random charging will have a great impact on battery life. Lithium batteries are basically packaged according to individual products, and are not common to each other. Therefore, each product also provides its own charging equipment, which is not common to each other, and can be used as long as they follow the respective instructions. Therefore, the introduction of battery charging in this chapter mainly refers to nickel-cadmium batteries and nickel-metal hydride batteries. There are two ways to charge nickel cells and nickel-metal hydride batteries, which is what we all know as "fast charge" and "slow charge." Fast charging and slow charging are an important concept of charging. Only by understanding the fast charging and slow charging can you correctly grasp the charge.