Patent ID: 8519671

Claim:
A charging device for charging a rechargeable battery, wherein the charging device comprises: a current source coupled to a power source and configured to provide a charging current to the rechargeable battery; and a controller configured to indirectly determine a charging state of the rechargeable battery by either varying an amplitude of the charging current provided by the current source selected from a maximum of two current amplitudes, measuring an output voltage at an output node of the current source and comparing the measured voltage to a voltage threshold selected from a maximum of two voltage thresholds, or by varying an amplitude of the output voltage at the output node of the current source selected from a maximum of two voltage amplitudes, measuring the charging current provided by the current source, and comparing the measured current to a single current threshold, and the controller is further configured to control the current source to provide the charging current with an amplitude that is less than the charging current required by the rechargeable battery in the determined charging state to bring the output voltage of the current source towards a battery voltage of the rechargeable battery.