Hand warmers can be roughly divided into three types: one is used to heat water, which is commonly known as hot water bags. Unlike traditional hot water bags, electric water bags save the trouble of adding water. As long as you plug in the power supply and wait for 10 minutes, you can heat up. In fact, it is to boil the water inside, so the temperature is usually very high. One is to generate heat through chemical reaction. The hand warmers on the market are of this type. The heat generated by the contact of chemical substances inside is about 40 ℃. The other is to use the lithium battery function. The internal heating pad heats up, and uses USB interface to charge and discharge, similar to the hand warming mouse pad. Because the lithium battery can charge and discharge, it can also be used as a mobile power supply. Small size, convenient to carry around, and the temperature can reach about 50 ℃. 1、 Lithium battery is used for power supply, with large capacity and more environmental protection. It can be recycled, charged for 3-4 hours, and kept at room temperature for 6-7 hours (the specific time depends on different models). Hand warmer Hand warmer II The latest ceramic heater is used inside, which is healthy, infrared heat transfer, promote blood circulation, accelerate metabolism, improve body immunity, and free of electromagnetic radiation. It is an ideal product for patients with arthritis, periarthritis, lumbocrural pain, rheumatism and rheumatoid arthritis, cold discomfort, cold limbs, cold pain in the wound and other pain relief and health care and winter warmth. III Small and lovely in shape, beautiful and generous in package, it is a good gift for relatives, friends and lovers. IV With USB reverse charging function, it can charge all kinds of digital products, which is suitable for home life, work and carrying out.