Need to load test the battery and see if you any drain while it’s setting. Also probably need to check volts when engine running. I find that story hard to believe also. This device will tell you exactly what you’re battery doing.
ANCEL BST200 or similar.
Amazon.com
https://www.youtube.com/watch?v=4kDc8gAypW4
If all else fails to find anything get bigger (CCA) battery. I sure they put the cheapest one they could buy in cart.