Abstract: Portable apparatus for charging a lead-acid battery from a direct current source such as a series of dry cells that can be conveniently carried in a motor vehicle or the like. An electronic circuit measures the actual current transferred to a battery undergoing charging and automatically signals when a preselected quantity of electric charge has been transferred to the battery undergoing charging. The electronic circuit means also signals that the battery undergoing charging has a preselected voltage level. The electronic circuit automatically signals that the direct current source has sufficient energy to charge a battery before a battery to be charged is connected thereto. The timing of the charge transfer is through the provision of charging and discharging a capacitor between preselected voltage levels by a current proportioned relative to the charging current and counting up a binary counter each time a preselected point in the oscillations are reached until a preselected count is reached.