I had the dreaded slow drain that drove me nuts.
car does low mileage and short journeys, it was on new battery replaced under warranty - no faults found. Great.
in a conversation with an auto electrician he asked the model of my battery: Lion, from a well known disty. Ah that's the problem, he said, bane of my life.
The disty, fair play, agreed with no quibbles to exchange under warranty and I opted for a premium brand and stumped up the extra £'s.
I can report that irrespective of lack of use, I have no more issues. I know this won't solve all issues...just another consideration.