I'm SO glad I looked underneath!
As I was getting ready to leave Les Schwab with the trailer wheel bearings freshly greased and repacked, I happened to notice something black hanging below the bumper.
It was the trailer battery! The bottom of the battery box had broken out and the battery was in the process of working its way towards the pavement.
I pulled the battery out and safely toddled back home.
I think this happened because I've been running a group 24 battery in the group 27 box - since the battery is a little smaller, it's entire weight is on the plastic bottom of the box - not reaching all the way to the metal 'shelves' that support the battery box. Guess I could get a welder to add a metal strip under the battery box to help support the battery.
So, one chore done and one more added to the list - not much progress today - but at least I didn't lose the battery (which is brand new).