Exactly what is a dc to dc charger?

[rvpopeye]

It's an isolator with extras.
Link to a Victron with descriptions of functions.

https://www.amazon.com/Generic-DC-DC-Charger-Victron-ORI121217040/dp/B0CWYWQGBF/ref=sr_1_2?crid=33NNH5N4WJ9GF&dib=eyJ2IjoiMSJ9.rzRLwb_Kriy4uAWzSWfsbEQIIOAmQpLXTlEgTwu4EcE5rDVyDYuUvi011X_79taWF_iKFublo8yIwTuMEXGrU6OGHXeBIL24Xc7kKihEdzFpAXmyPmJFtL1iRvjdtSFjOpfJJFUUWVkp8xgv4B6x1Ezi6yYlBeHvmfTnwSBqhuTcyNcaNwp-2fihk3IgRNpIf47P6CK-0vejPGKEhxiAGpsarQQlYY1Dt3a6Qhx2VdDWwpN5F9s1uRDL-thuLH77Recx7FbnOnCBxwPDlxsRSEdiN6XSHblFfJkQbLY13LM.QU12A0P2DPlYVWvS_MsSOIqzmLUlWivFH8XYFYNv0xo&dib_tag=se&keywords=victron+dc+to+dc+charger+12v&qid=1728869749&sprefix=victron%2Caps%2C322&sr=8-2