2005 Chevy Avalanche Gremlin high beams

About 2 months ago I had 35995 miles on my truck and took it in fore its last warrantee repair which included the collapsible part of the steering column, which they replaced. About 2 weeks later and no out of warranty, my battery was dead in the morning. The neighbor told me my headlights were on in the middle of the night. The same thing happened the following night. The third night my neighbor called at 11:00 pm and told me they were on ugen. So I went out to investigate. The high beams were on but no taillights or any thing ells, just height beams. I tried everything to try to turn them off but nothing worked! Eventually the battery died. I charged the battery and it was fine. For about an hour when they came back on. At this point I unplugged the high beams and all was well. (Just no high beams). A month later now the weather is colder and my battery is dead every morning. I suspect the battery is no good now? Does that sound right? I return the truck to the dealership and they refuse responsibility. And they warned me that it will be”a hard one to diagnose” because it only happens at night when there not at work.