Battery for automotive electrical system

A battery for automotive electrical system comprising:

• a lead battery having an outer shape of a rectangular box, and having the length (L) thereof which is longer than the width (W) thereof;
• a sub-battery being connected in parallel to the lead battery;
• and
• a first main terminal as a positive electrode terminal and a second main terminal as a negative electrode terminal being disposed at both ends adjacent to a long side on an upper surface of the rectangular box,
• wherein the first main terminal as an output terminal is connected to a lead wire for a vehicle, and the second main terminal is connected to the sub-battery,
• wherein the sub-battery has a structure in which plural cells are stored in an outer case, and the outer case is disposed outside an end portion in the lengthwise direction of the lead battery and adjacent to the second main terminal of the lead battery, and the lead battery and the sub-battery are coupled.