Damned if I can think of why there is a place for a second battery under the hood of the 1997 Checy Tahoe I drive: there is nothing about it in the owner's manual. This is yet another mystery, along with calculus and women, that baffles me.
Is there any reason for putting a second battery there, other than to jump-start the primary if and when necessary? If so, how does the second battery stay charged? And is there such a thing as the femal orgasm?