My experience from leaving a wireless OBD plugged in (by mistake) was a significant battery drain. I searched and searched for the parasite pulling fuses and watching my multimeter and finally narrowed it down and found I left that dang wireless OBD plugged in. If you drive the car regularly probably not much of a problem but when mine was plugged in the parasite increased my draw from the battery 2-3x the norm sitting and shut down.