Charging Method, Device, and System

The present disclosure provides a charging method, device, and system. The charging device includes a voltage regulation circuit, and can charge a charged device through voltage step-down or voltage step-up. In addition, the charging device and a charged device can transfer statuses of a circuit and a battery through a change of a switch status, so that the charging device can regulate a charging voltage and/or a charging current based on the statuses of the circuit and the battery.