If your model is like mine, there is a battery disconnect switch. Mine is inside my pass-thru storage. If you are planning on going out again in a few weeks, i wouldnt worry about the batteries, they will be ok.
Same for the water system. You generally only need to drain things when winter sets in and freezing weather is coming. Then you winterize the trailer by flushing out the lines and adding some RV anti-freeze to them(or use an air hose attachment and blow them out) and your pluming drain traps.
'09 F-350 6.4l Crew Cab
'10 Komfort Trailblazer T262BSLE