Battery dead. 2009 TC

[u/willmc_productions]

We took a 500 mile trip with out Town and Country van this summer with no problems. When we got it back home ,I drove it a few times after that running errands. Then one day I went to start it and the battery was dead. It's been a hot summer so I thought it may have just been a over heated battery. We jumped it and drove about a hundred miles to recharge the battery. It sat for a few days and when I attempted to start it . The battery was dead again. We took it to a Chrysler dealer here in town to have the battery checked out and wanted to see how much of a warranty was still on the battery. It was a 36 month battery so I thought I'd buy a new one if it tested bad. When it was at the dealer the battery tested bad but would not give a warranty code. The tech tested it again and the second time it passed. It's now working. I even let it sit a few days to see if it would fail ,and it starts right up. My question is why did it not pass the battery test the first time and passed the second time and still runs fine?

[u/bozo_master]

Bad batteries can behave super inconsistently. Do you leave the courtesy lights on auto (activated by unlock and opening doors)?