For example, people worry about leaving disconnected chargers plugged into the wall for fear that they’re draining power. Are they right? Heat flow analysis provides a simple rule of thumb: If an unused charger isn’t warm to the touch, it’s using less than a penny of electricity a day. For a small smartphone charger, if it’s not warm to the touch, it’s using less than a penny a year. This is true of almost any powered device.
