The following is my simple calculation, not necessarily correct, please look at dialectically:Preparatory knowledge:1)? ? W=qU? ? That is: electrical work (J)= charge (A)× voltage (V)2)? ? W=Pt=UIt? ? That is: electrical work (J)= power (W)× time (t)= voltage (V)× current (A)? Time (t)Take a 4000mA·h (charge q) mobile phone battery as an example:Assuming that the charged electricity (work done by electrical energy, electrical work) is all converted into the stored energy (chemical energy) of the battery, that is, the efficiency is 100%, and q=It can be simply deduced (originally there is this formula), then:t=q\/ISo you have to know the charging current, the general 18W mobile phone charger says 5V-3A,8V-2A,12V-1.5A. Which one? A 5V-3AT = 4000 ma · h \/ 3 a = 4 a. h \/ 3 a = 1.33 hThat is, if the charging current does not change with time, it takes 1.33 hours to fully charge a 4000mA·h battery.Again, it may not be true, it may turn out to be true, but there is something wrong with the meaning