You don't say how many days it takes to discharge, but the newer units have more parasitic draw, than the ones from the old days. Another thing...often times the lighted displays showing state of charge, are not accurate. You need to check full voltage with a digital volt meter, and check each day after for the amount of loss. Within a week or so, many campers, with a single battery, can be discharged below a safe level, while parked non-use.
Jerry