Systems and methods for determining battery capacity in portable electronic devices are disclosed. In one embodiment, a method for determining battery capacity in a portable electronic device may include: (1) disabling battery charging for the portable electronic device; (2) measuring a voltage and a current across terminals for a battery installed in the portable electronic device; (3) calculating a voltage offset across the battery using an estimate of an internal resistance for the battery by multiplying the current by the estimate of the internal resistance for the battery; (4) calculating an estimate of the open circuit voltage for the battery by subtracting the voltage offset across the battery calculated from the measured voltage; (5) retrieving a battery capacity based on the estimate of the open circuit voltage; (6) quantifying the battery capacity; and (7) displaying the quantified battery capacity.