The second battery, like factoring large numbers

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?
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One reason would be that one of the optional engines was a Diesel which would require two batteries in order to supply sufficient starting power.
Another reason would be an optional snow plowing package that included a second battery because the electric over hydraulic plow units tend to consume a lot of power.
A third reason would be a towing package that included a second battery to power a travel trailer.
The second battery stays charged because it is; connected directly to the alternator in the case of the Diesel, or, connected via an isolation relay to the alternator in the case of the plowing or towing package.
Can't answer your last question since it merely appears to be a bad joke gone wrong...
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Hi!

At least this mystery has a solution. If you had a diesel engine in there (did they offer one in the Tahoe?), you'd have a second battery as well. Maybe it's a vestige of something that would be more at home in a pickup truck.
The batteries are wired in parallel, so the alternator charges them both and only ever sees a really large twelve volt battery.
On my '84 GMC Sierra (6.2L diesel), the glow plugs take their power primarily from one battery while the starter seems to pull more on the other. And having a 78 amp alternator to charge up two 1000CA/900CCA batteries is a joke.
William
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