Because a charger is a transformer with a primary coil (input), and a secondary coil (output), along with a rectifier to convert to DC, as long as it is plugged in, the primary coil is using energy.
We all know to unplug our cell phone when it's fully charged. The charger has two ends. Does it use energy, when it's plugged into the wall, with no cell phone attached? I would think not, with nothing attached to draw current.

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