Jason, this is mostly a matter of how you look at it.  I'll try to explain
below.

At 22:32 8/12/99 +0000, Jason M. Yasment wrote:
>4.  Run an 8 or 10 ga wire from the + terminal on the aux battery to
>terminal #30 on the relay. This terminal supplies current to charge the aux
>battery when the van is running.
>4a.  What the diagram shows when the relay is closed is that it will charge
>from the starting battery, drawing that battery down and reducing it's
>useful life.  Then the alternator would charge the starting battery the
>energy that was used for replenishing the aux battery.

The relay puts the two batteries in parallel, and if the alternator were
not charging then you're right, the battery with more charge would
discharge into the other.  However (this is the point of the relay), the
alternator *is* charging b/c the relay would not have closed
otherwise.  Now the alternator brings the system voltage up higher than
either battery can supply by itself, and both batteries charge
simultaneously.  Whichever one is more discharged takes the most charge,
which is exactly what you want.

>  The starting battery
>can only recharge the aux battery with what ever energy it has and will not
>fully charge unless you drive for a few hours.

This is true, but not for the reason you say, i.e. it takes several hours
to fully charge a discharged battery.  In fact the last 15% of charge will
take about 2 1/2 hours all by itself.  This is partly the way batteries
work, and partly because the regulator (like all automotive regulators) is
a simple design that expects the battery to be almost fully charged all the
time.  The 15%/2.5 hours is unavoidable.  However, the charging up to that
point could be made a good deal faster by installing an (expensive)
marine-type regulator which expects to work with deep-cycle batteries.

>   In the mean time you will
>only put a substantial drain upon the starting battery and still not fully
>recharge the aux battery.  In other words the aux battery is not directly
>charged by the alternator in this configuration.

No, it really is.

cheers
david

David Beierl - dbeierl@ibm.net