Not sure if it was a "freak" occurrence, but on ONE occasion, I finished charging the battery and disconnected the charger from the wall, but NOT the battery. To my dismay, the battery drained with this arrangement. I wonder if this might happen when the timer cuts power to the charger. I have not replicated this incident (for fear of battery damage), but nowadays, I always disconnect the battery from the charger once fully charged. No more phantom drain.