You did no damage to trailer or battery. If you damaged the battery, it would have blown the top off. I just lay a rag over the other terminal keeps that from happing as stated always hook up ground last. And use safety glasses when working with batteries.
I did the same thing last year, wrench across the two battery terminals. Scared the hell out of me. No battery damage and no damage to the trailer wiring.
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Jeff
Lindsay, Ontario, Canada
2021 East to West Alta 2600 KRB
2020 F-150 Lariat 3.5L EcoBoost