Various embodiments of the invention relate to a battery charging system that enhances the charge rate and reduces the charge time for a battery applied in a mobile device. The battery charging system is provided with an adapter output voltage, and generates a battery charging current to drive the battery. This adapter output voltage is controlled to vary within a reference voltage range which is narrowly controlled to include and track a preferred adapter voltage. The battery is therefore driven by the battery charging current that is associated with a preferred charging current under a preferred charging condition. The battery charging process may be completed under a condition that is substantially close to the preferred charging condition, allowing an enhanced battery charge rate and a reduced battery charge time.