Do USB power supples use power when not plugged into anything?

I have a little 12 volt battery and I am going to connect a car charger usb power adapter to it.  My question is: do they consume even the tiniest amount of power while plugged in but not connected to a usb device.  Will it drain my battery parasitically? Thanks  

jeff-o6 years ago
Yeah, it'll drain your battery. At what rate will depend on the charger; some are better than others.
Yes the battery will drain the battery but it's slow enough that it shouldn't be a very big problem as long as you don't mind charging the battery once and a awhile.
orksecurity6 years ago
Yes, and yes. The question is whether the drain is enough that you'd ever notice it -- and that depends on just how "little" your battery is, as well as exactly which charger you're using.

If you don't want to bother with putting an ammeter on it, I'd suggest you just try it, see how well the battery survives, and if the drain bothers you add a switch between the battery and charger. Or just add the switch on principle.
Yes, it will drain your battery, but not very quickly.