Abstract: Methods for charging batteries comprises applying a charging current to the battery, monitoring the voltages of the positive and negative electrodes during the step of applying the charging current, and determining a point during the process of applying the charging current where the negative electrode is fully charged. Monitoring comprises determining the total battery voltage from the combined voltages of the battery positive and negative electrodes. The slopes along the total battery voltage are measured to obtain a trend line of the change in the slope of the total battery voltage during charging. The trend line is monitored against a logarithm of the applied charging current to determine a point where the negative electrodes are in a state of full charge, at which point the positive electrodes are also fully charged. The charging operation is terminated once such state of fully charge has been determined.