Description: ABSTRACT OF THE DISCLOSURE: An electric storage battery for motor vehicles is composed of two subunits which are a main storage battery and an auxiliary storage battery. Both subunits are interconnected by a switch which, in one operational position, disconnects the auxiliary battery from the main battery and connects it directly to ignition terminals of the ignition system of a motor vehicle. Thus, the spark plugs of the engine receive the full voltage of the electric storage battery undiminished by voltage drops such as caused by operating the electric starting motor of the system. Thereby, the disadvantage of starting difliculties experienced with motor vehicles having normal electric storage batteries in cold weather is successfully avoided. The main unit has U-shaped plates, and these define a recess in which the auxiliary unit is received.