I charge the batteries up to 100 % and 4-5 days later they are doown to 62-64 % with absolutely nothing turned on……
Suggestions?
It would be helpful to have a digital ammeter showing the entire boat consumption, but if not, you'll have to wait a few days to check for drainage.
Start with the extremities, so to speak. Right now, all breakers on and all appliances in the OFF position. Drain ?
Next, all breakers and all appliances OFF but main DC breaker in ON. Drain ?
Next, all appliances, all breakers, and main DC breaker OFF. Drain ?
Next, all above OFF and house battery selector OFF ........................
........................ and keep going from there until you disconnect the house batteries as your last OFF. It won't pinpoint the leakage but it definitely narrows it down.