Hi, there may be devices like a propane alarm that are still powered even when your use/store switch is off. The best way to ensure the batteries are not connected to anything is to install a battery manual disconnect switch at the battery terminal. If you search the forum (you must be logged on) you can find inexpensive manual battery disconnect switches that other owners have used. I would also verify with a voltmeter that your batteries are charged and that they are being charged when on shore or gen power. Check water levels if they are wet cell batteries also.
Regarding your water pressure reduction at the kitchen sink only, I would ask if this has always been an issue (you have a 2018) or just started being a problem? In some coach models slides have caused water line pinching (typically a problem from new); but if this is just a recent problem it might be something as simple as water carried debris plugging the tap aerator; or valve body. If your kitchen sink uses a separate hot and cold tap, is one or the other or both hot and cold affected by reduced flow? If the tap is a single handle style and both hot and cold are affected then suspect a valve body debris restriction (if slide position is not causing a restriction kink on both hot and cold water feeds). The easiest first check is remove the tap aerator and check for bits plugging the flow. Some folks have also removed the water feed lines to the taps (cold if just cold water is the issue) to see if flow is normal to that point.