With the original charger, if your phone is still not charged, then you can change a charging cable to try, if still not, it is likely to be the phone itself has a problem.
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1, the battery is excessively worn or completely damaged
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In general, this situation is relatively rare, you can check the health of the battery first. For the average iPhone, a battery health rate of more than 85% in one year and more than 75% in two years is normal. But if you're down 80 percent in one year, there are only two possibilities. One is that you're buying a fake, and the other is that you're doing something to damage the battery. I have seen some people, because the card game almost every day to charge several times, as a result of less than half a year, the health of the mobile phone battery has dropped to 78%.
Charging cable connector is broken socket contact poor phone USB port contact (can be connected to the computer to try) plug power is not enough (such as ordinary plug to charge ipad class) carefully check.