1, you can check the charging interface, sometimes the interface is not close to the charge will not go in.
2, if all checks are correct, there may be a problem with the magnet.
3, there may be contact oxidation, use a needle to clean the contact.
4, before plugging in the charging cable, ensure that the charging cable and charging head are good, some charging head and the watch USB seat with poor contact, to use the watch with the charging cable.