Hand warmers can be roughly divided into three types: one is to heat up by heating water, which is what we commonly call a hot water bottle. Different from traditional hot water bottles, electric hot water bottles save the trouble of adding water, just plug in the power supply and so on. It can heat up in 10 minutes, and it actually boils the water inside, so the temperature will generally be very high. One is to generate heat through a chemical reaction. The hand warmers on the market are of this type. The heat generated by the contact of the chemical substances inside has a temperature of about 40°C. The other is to use the lithium battery function, the internal heating plate generates heat, and uses the USB interface to charge and discharge, similar to the hand warmer mouse pad, because the lithium battery can be charged and discharged, it can generally be used as a mobile power supply. Small size, easy to carry, the temperature can reach about 50 ℃.
