Battery charging system and method

A battery charging system enables rapid recharging of a working battery without immediate access to ac power and without the need for current limit and/or overvoltage protection. The battery charging system makes use of a charging battery having a number of cells that is greater than the number of cells in the working battery. The charging battery produces a charging current that is proportional to the difference in the number of cells in each battery. In this manner, the battery recharging system is capable of rapidly recharging the working battery. The number of cells in the charging battery is selected, however, such that the series voltage of the charging battery cells is less than or equal to the maximum rated voltage of the working battery. Thus, the voltage of the charging battery is greater than the operating voltage of the working battery but less than or equal to the maximum voltage rating of the working battery. As a result, the charging battery is generally incapable of overcharging the working battery, and therefore does not require current limit and/or overvoltage protection circuitry.