Renogy 40 Amp DC-DC ("B2B") charger.  I bought this for a van build, but ended up using a different charger and can no longer return it.  Still in the original box, never opened.  MSRP $200.

$100 shipped.

Here is some more info about the unit: renogy.com/12v-dc-to-dc-on-…

Manual: renogy.com/content/Manual/D…