More on the proper application of a DC-dc convertor

We have learned that the DC-dc convertor being rated at 99.9A@12Vdc output is actually capable of much more and in the mode we are running it does not self limit.  Therefore we need a circuit to limit the flow between the DC-dc and the lead acid battery while not limiting the DC-dc to Car, or Battery to Car.

Our learnings suggest that if the DC-dc is connected straight to the battery at 12.xV charge, the DC-dc will output as much as it can to bring the battery up to 13.2V instantaneously.

As is today.

Circuit below is shown same as above, but needs to be changed for the wanted operation.  An on-board DC-dc RV charger has been suggested.  Other suggestions?

Wanted:

1.  OEM lead acid OR DC-dc should be able to run the OEM fuse panel.  Currently the car goes completely dead including the windows, locks, charging port release, and alarms.

2.DC-dc should support/float the OEM battery during driving.

3.The DC-dc should shut ENTIRELY down when not driving to reduce OEM battery drain.

4.DC-dc can be on during charging, but when charging completes it should shut down to avoid drain.

5.DC-dc should start after clamping and shutdown before Main relays release to avoid wielding.