What will happen if I leave my ZUS plugged into the car for a long time?

When ZUS is not charging other devices, it consumes less than 0.02A. The battery for a normal car is around 50~60Ah. Let's say there is only 50% battery power remaining which is 25~30Ah. It would take 1250~1500 hours（52-62 days) to drain your car's battery, assuming you do not drive the car at all during that time.