External battery charger for use with a battery powered electronic device and an extra battery

A method of charging a battery through an external battery charger which supplies power from an AC adapter both to a portable electronic device and the battery, the method comprising the steps of:

• detecting a load current consumed by the portable electronic device;
• determining whether the detected load current is approximately equal to a maximum current rate set in a DC input line of the portable electronic device;
• determining the ratio of the detected load current and the maximum current rate;
• and
• determining a charging current rate supplied to the battery such that the amount of charging current is equal to a remainder of the power used by the portable electronic device.

A battery charger for supplying power from an AC adapter to both system components of a portable electronic device and a rechargeable battery, the charger comprising:

• a charge regulator for controlling an amount of charging current being supplied to the battery;
• a load current detector disposed in a power supply line connected to the system components of the portable electronic device for determining an amount of current drawn by the portable electronic device;
• a microcontroller, in response to the amount of the load current detected by the load current detector, producing a first control signal representing the load current being approximately equal to a maximum current rate designated by the portable electronic device and a second control signal representing an amount of charging current being supplied to the battery, the second control signal being supplied to the charge regulator for charging the battery with the remainder of the power used by the portable electronic device;
• and
• a switch disposed between the DC input port and the charge regulator for interrupting a power supply line connected to the charge regulator, the switch being responsive to the first control signal from the microcontroller.