I have the same 20A Renogy DC-to-DC charger, and am in the process of getting things wired up in my Ford Transit. FWIW, my experience with Renogy has been absolutely terrible. As the OP mentioned, the manual is very vague. While the Tech Support people I've talked with have been friendly enough, the information I have received has been inaccurate more than it has been correct. That's IF you can reach someone (e-mails go unreturned, so a phone call with a 15+ minute wait to talk to a human has been consistent for me). When I pushed back on the (inaccurate) information I was told based on industry standards, etc., the (first-level) tech support guy I was talking with consulted with an engineer, and confirmed that my assumptions were correct, and tech support's initial information incorrect. This is a HUGE deal in regards to customer safety, IMHO.
MOST IMPORTANTLY...
After talking with George at Renogy (Tech Support Supervisor), he told me that, at least in regards to Lithium Iron Phosphate batteries (which I have) [font=Tahoma, Verdana, Arial, sans-serif]the DIP switch settings[/font]are incorrect in the manual. He said they're working on correcting the manual, but it would be at least a month before this was done. My internal question after hanging up the phone was, "Why doesn't Renogy e-mail customers who have purchased the charger and let them know this?!?" I e-mailed the tech support e-mail suggesting this, and got no response, which is consistent with a couple previous e-mails I sent to Renogy.
I got the correct switch settings over the phone, but I would double-check with Renogy via phone tech support. Enjoy the hold music while you wait, then hopefully you get someone competent who can give you accurate information.
As you can probably tell from my tone, I'm absolutely less than impressed with Renogy, and I haven't even got my Renogy charger or battery hooked up yet. I won't be giving them any of my dollars moving forward. I did have a good, honest-but-respectful conversation with George (again, the Tech Suport Supervisor), and he indicated that they have had some turnover/staffing issues, and are supposedly working on improving service. Time (and the market) will tell, I guess.
Craig