I have a 2015 Transit SMB RB50 built in Fresno. It's Transit serial No. 001 for them.
I just checked and I have a 7620 installed and there is a push button under the dash near the steering column that I was told that I can push to start the van off the house battery. The 7620 is installed on a board under the bench seat on the passenger side.
My van is in storage a lot, (only 25K miles on it). I typically leave it plugged into shore power full-time with the main house breaker off. It must be maintaining the van battery as well as the house because I haven't needed to replace either battery, so far, after 6 years, (Knock-on-wood). My UB122000 AGM house battery is starting to show some reluctance to staying charged when I'm on solar on a trip. Like me, not what it use to be.
It sounds like my systems are working like they are supposed to be.
Thanks to Scotty for that video link. That explains a lot, including the 'thud' noise I hear sometimes coming from under the bench seat.