my guess is aftermarket. Was this purchased new or used?
i don't have one, and I don't recall ever seeing such a thing in the options list....
You say small, so my guess is it's one of those trickle charger panels. I'll bet if you look at the batteries, you'll find the small gauge wire leads coming from the panel, or controller if there is a separate one, landing directly on the batteries.... either the house battery(ies) or the chassis battery.
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