The battery did have enough charge to power my 12v lights but not enough to power my new LED replacement bulbs.
Impossibility.....the LED's draw 1/5 the current of the incandescents they replace. You have something amiss.
Anytime I buy a used battery, I consider it to be suspect. I'd suggest to take the battery to an auto parts store to be checked. When you do this, you can clean up the connections.
BTW, a hand held meter is going to be a good tool to have on hand for your RV. Cheap ones can be bought at Harbor Freight or any of the big box stores.