I don't think there are many, or any, of the old single stage chargers coming on trailers less than 10 years old. The market got wise to that long ago. And multi-stage chargers got very cheap. The good news is you almost certainly have a multi-stage. The bad news is it is probably a WFCO brand. They work, sorta. Many won't want to go into bulk mode. So you never get a full charge, and it is bad for batteries over time. There are better replacement converters for just about any trailer.