YOu have given very little to go on here, but I will run something at you that you can treat as free advice....
First, are you sure the batteries are draining and not just junk??
To answer this, get the bank as charged as you can do easily and disconnect the bank COMPLETELY. It need only be one side and positive or negative it does not matter. If the bank is made of paralleled jars, break them apart. Let it(them) sit for an hour or two and measure the terminal (means at the battery bank) voltage with a decent meter. Come back in a day and check them (it) again. If they have dropped much (ie below 12.5) in that time, they are sick.
Assuming the bank is good, but you are still seeing a phantom discharge, get a little light bulb, two alligator clips and two pieces of wire. Build the kit so you have a clip on light bulb.
Put you new little test light between the bank and the house. There should be nothing else attached to the house bank terminal.
Does the light - Light?? If yes, you have a drain.
Keep pulling fuses until the light goes out.
I did a lot of this when I did all kinds of boat work before the depression killed it. I still have my little light bulb.
A lifelong waterman and his bride going dry places for as long as the fuel money lasts.