First we gotta define significant, I guess. I'd guess the total load of
4 fully charged batteries  to be a tiny fraction of the 120 amps,
though, maybe 12 amps. It's not the alternator that you are paying for,
but the load. disconnect the other 3 batteries, and the 120 Amp
alternator likely costs no more power than the 70 amp one.
Al Brase

John Connolly wrote:

>I should point out that a battery is a load to an alternator. Adding
>additional batteries increases the load (and drag) on the engine, even if
>they are fully charged. A fully charged battery is a significant load to the
>alternator.
>
>John
>Aircooled.Net Inc.
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