This compact and robust unit brings the two voltages either of the on-board battery or the starter battery at the display. It depicts the range of the battery voltage from the deep discharge up to the maximum charging voltage. The illuminated dot display generates nearly an exactely display of the battery voltages. As per keypress the on-board or starter battery will be choosen or the display will be switched off. At low battery voltages a red display indicates that a reload becomes due. The connection will be made by screw type terminals at the back side of the unit. Minor front panel dimensions and the especially small installation depth of only 15 mm allow the mounting at nearly any part, so that space behind it can be used for storage.