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Quick answer: yes but most drain so little you wouldnt notice if the car is driven at least 3x a week.
Longer answer: depends on the dongle but in most cases yes. ODB2 standard puts constant power to the port (there is always power there even if key off, car parked). Most dongles are on when plugged in, and only turn off when you unplug it. So it will be on all the time and a small drain on battery, especially cheaper dongles where they make the circuitry as simple/cheap as possible. Some dongles small drain, some larger. I've seen some high end wifi dongles that detect when the car is off and turns itself off thereby not using the constant power source even tho it is there, and thereby not using power when car is off. If your car driven once a week or less, I'd unplug it. Most the cheap dongles would take 2-3 weeks to drain a new good battery in summer. But constant drain and recharge will shorten the life of a battery. And why deal with it in very cold winter or when your battery is older and towards end of life and now you have a jump/charger situation just for a dongle
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