Experts have determined how much electricity is used to charge an average smartphone, or when an unattached charger is left plugged in to the wall. A study also revealed the dollar amount it costs per year to charge a device.

In today's technology age, many people have added a new item to our to-do list before going to sleep every night. Besides brushing our teeth, washing up, and making sure all the lights are turned off, we also plug in our smartphones and electronic devices and let them charge overnight. In the morning when we awaken, ready to face the day with our bodies fully recharged, so are our devices.

But it only takes the average smartphone two hours to actually get a full charge. Are we wasting electricity and money by leaving our smartphones plugged in longer than that?  And what about when we just leave the charger itself plugged into to the wall, without anything attached?

According to experts, you can sleep sound with that charger or phone plugged in and not worry about what it's costing. Cambridge professor David MacKay says unplugging the unattached charger from the wall over a full year will save you the same amount of energy as it takes to run one hot bath. If the phone is attached, that energy use multiplies tenfold, but is still so minimal as to be considered negligible. According to MacKay, "Obsessively switching off the phone charger is like bailing the Titanic with a teaspoon. Do switch it off, but please be aware how tiny a gesture it is."

A study by the Lawrence Berkeley National Laboratory showed that simply plugging your charger in the wall used an average of just .26 watts of electricity. With your phone attached and actually charging, that number grew to 3.68 watts. Once the phone is fully charged, the electricity usage drops back down to 2.24 watts. All of these numbers are relatively small, however, as the study concluded that the average cost to charge a smartphone for an entire year is just $5.30.