Positive and negative connection will of course damage the battery and charger, serious words will explode; However, some chargers with better quality on the market now have positive and negative reverse connection function protection; If the connection is reversed, it will automatically disconnect the electricity and will not cause an explosion.
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The power supply IC or the protection circuit of the power supply burns out (if you are lucky, you will burn the fuse\/safety resistor).
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If the design of the phone is not good enough, other components of the motherboard may also be burned.
The battery connection protection board is made into a battery holder, and then the electric wrench is connected. If the positive and negative electrodes of the battery are reversed, the battery protection board will be burned instantaneously.