1, the maximum limited charging voltage of lithium-ion batteries is about 4.2V, and the minimum limited discharge voltage is about 2.5V, which is achieved through the protection circuit inside the battery and cannot be manually controlled. When the voltage of the charger is 5V and the battery is 4.2V, the battery can be fully charged. If the charger voltage is also 4.2V, there is no voltage difference between the battery and the charger, and there will be no current through. When the voltage at both ends of the battery is 4.2V, the inside of the battery is automatically converted from the original normal charging to trickle charging, which will not damage the battery.
2, the mobile phone charging jack is broken, take out the battery, install it on the universal charger and charge it directly. Do not try to connect two lines out of the charge, if the power is reversed or the voltage rises, it only takes 1 second to make you regret it. Before the battery is charged on the universal charger, it is necessary to understand the instruction manual of the universal charger to ensure that the battery is not connected to reverse polarity, and then it can be connected to the mains for charging. For the so-called \"automatic conversion of positive and negative poles\" function, it is a lie to the dead, do not believe that the function is at most able to detect the positive and negative poles of the battery, and automatic what is far from what, this misdirection is more likely to make the battery due to contact but lead to scrap.
The third question does not need to be answered.