My new TAB battery was discharging within a couple of weeks when in storage. I learned that there are (apparently) enough sensors and such running all the time to discharge the battery. Mine went from 12.5 volts when first parked to 11 a week later and then disconnected.
My two part solution has worked well for me now:
1. Add a battery disconnect switch ($7 https://www.amazon.com/gp/product/B01IQRMFWY/ref=oh_aui_detailpage_o03_s00?ie=UTF8&psc=1
) and disconnect each time you park.
Apparently new TAB's already have a battery disconnect switch so this may be unnecessary for you.
2. Add a $40-$60 5 watt trickle charger while parked. (https://www.amazon.com/dp/B0006JO0TC/ref=sr_ph_1?ie=UTF8&qid=1485546201&sr=sr-1&keywords=Sunforce+50022+5-Watt+Solar+Battery+Trickle+Charger
I have photos but I don't know how to add them. LOL Best wishes. -Deac