Is your optica battery guy a salesman? If he is, that might explain it. Most salesman don't know diddlysquat (I wander what spell check will come with up for this word) about technical issues. Just ask a car salesman some technical questions about a car he is selling to prove my point.
When the voltage from the alternator, battery charger or any other DC source is the higher than the voltage of the battery, the current will flow into the battery and it will charge. If the voltage of the source is lower than the battery voltage the current will flow out of the battery and the battery will discharge unless the current is not reversible such as in a battery charger. In the old generator systems, the generator had to be protected from battery current flowing back thru it. This was done by a "mechanical diode" in the voltage regulator box. This doesn't happen with alternators because there are solid state diodes in the alternator which prevent reverse current flow.
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