A digital controlled battery charger comprises a power converter, a voltage sensor, a current senor, a mode selector and a digital controller. The voltage sensor and current sensor detect the voltage of a rechargeable battery and the current flowing through the rechargeable battery respectively. The mode selector selects a feedback signal from either the output of the voltage sensor or the output of the current sensor. The digital controller receives the selected feedback signal and generates a pulse width modulated signal for the power converter. Additionally, the digital controller is capable of dynamically adjusting its coefficients so that the control loop can maintain a stable system when the battery charger operates in different battery charging phases.