Just as a bit of a follow up to the flat batteries issue, both the battery in our Lexus and the one in the Camry gave up the ghost in the last couple of weeks. The guy from RACQ said it is happening a lot at the moment due to cars not being used during Covid19. The Lexus battery was even still under warranty. Imagine that, something giving out while still under warranty! Anyway, before he left, I thought to ask him about the boat batteries. He said it was definitely possible that batteries could flatten over a month or so if a circuit was open. He said modern devices have a discernible drain if left on.