Your other batteries charge in the same mod successfully and work when left overnight? If so, your battery is just old and won't hold a charge any longer.
Six months of daily use--figure 180 charges--is kind of low, but not terrible depending on how much you stress it. Using that many batteries in that many mods, however, implies that it got a lot fewer charges than that. It probably wasn't a great battery to begin with, unfortunately.
If other batteries also drain out overnight when left in the Kanger, something's awry in the mod. Maybe you can fix it, but you'll probably have to replace it.