Abstract: A charging circuit includes a programable CPU for supplying a constant voltage and a constant current respectively to a voltage control circuit and a current control circuit so as to obtain function of automatically adjust the charging voltage and fix the current. A voltage checking circuit is provided to coordinate with the CPU for keeping watch of charging operation and checking if a battery being charged is normal or not. If the stored electric volume is less than a quarter (indicating the battery is damaged), if the positive and the negative of the charging circuit are connected reversely with those of the battery, if pinchers of the charging circuit contact each other in a short-circuited condition, or if the pinchers fall off the poles of the battery, the CPU stops at once charging operation so as to protect the charging circuit and batteries.