I did a current test last night. Hooked up ammeter in (-) line. Initially draw was about 1500mA, but over the next few minutes this decayed to 800mA, then 500mA. After 10 minutes it was reading between 10-15 mA, so essentially nothing. I checked whatever grounds I could find. All good. The battery seems strong. I suspect that intermittently, during shutdown sequence, something is going wrong and leaving some system powered. As this has happened only twice it will be very difficult to isolate, as doing anything to the vehicle wakes it from its standby mode and will likely change the state of whatever was wrong. I have taken to using the battery isolator for overnight parking.