Reg/Rect output ok but not at Battery

A test that would have verified it early on is to put a DC ammeter in line with the regulator to battery. That would have told you if there was charging current or not. Some of those cheap meters have amps too, but you'll need at least a 10A range if not more. I'd go for 20A and make sure the 17A fuse in in place to be safe. Charging current (or lack thereof) could be measured on either side of the fuse. Ammeters do have a place.