When the charging is completed the charger cools down to less than hand-warm. It's still not entirely cold, so I guess it's using a fraction of a watt. But as all my heating is done by electricity anyway (no gas or oil) it doesn't matter one bit at all, even if it used fifty watts.

But I don't leave anything plugged in at home when I leave the building, unless it's unavoidable. Had a fire once, fortunately when people were looking directly at it when it started.