Can be used, the lithium battery is 3.7v full is 4.2v, simply put, you must be higher than 4.2v to be full, just like the water flow to the bottom of the truth is the same, only the charger voltage is higher than the battery voltage, it is possible to charge the battery inside; And the charger must have a surplus, the electricity can be charged in, there is a loss on the line. In fact, mobile phones and other electrical loads, there is a special IC to control the lithium battery charging, the 5V voltage is only supplied to this chip and the related control circuit, by this charging circuit to control the charging, and not directly let the 5V voltage connected to the lithium battery