The present inventions, in one aspect, are directed to techniques and/or circuitry to applying a current pulse to the terminals of the battery during a charge, measuring a voltage at the terminals of the battery, selecting a relationship of an open circuit voltage to an amount of charge in the battery using data which is representative of a state of health of the battery, calculating an open circuit voltage of the battery using the voltage measured at the terminals of the battery, a current applied to or removed from the battery and an impedance of the battery, and determining a state of charge of the battery using (i) the calculated open circuit voltage and (ii) the relationship of the open circuit voltage to the amount of charge.