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Different converters used different schemes to keep the gen battery charged and deployed the big oil cooled alternator in different ways. If you have two alternators, one 12vdc and one 24vdc be sure you know where any line from your 12vdc alternator goes and be sure the Li batteries are isolated from the La batteries via a BtoB charger. Check carefully any “boost” wires/switches. Some converters used the big oil cooled alt as a 12vdc house charger and the separate 24vdc air cooled alternator as the charger for the chassis batteries. Others apparently reversed those so check carefully. A 12vdc BtoB charger needs 12vdc on the input side to turn on and a rise in voltage from the alternator running to pass charge current on to the Li batteries. If you are trying to charge a 12vdc Li bank from a 24vdc alternator you need more engineering than can be done in a few sentences.
Jerry