Do you feel bad charging your iPhone at your friend’s house?  You shouldn’t. It costs about $0.25 per year to charge.*

Here’s where we use our energy now (ish) vs. 1978. Interestingly, the total energy use is the same (10.58 vs. 10.55 quadrillion Btu) even though we have more population, more houses and bigger houses.  We have many more appliances and devices that use energy. The energy efficiency of our appliances and devices, including our furnaces and A/C have drastically improved.

*An iPhone 6 has an 1810mAh capacity battery or about 6.85 watt hours. Draining it fully and charging it everyday would use about 2.5 kWh per year.  The average electricity cost in the U.S. is just over $0.10 per kWh. So, charging your iPhone 6 everyday costs $0.25 per year.  Wow.

Source: http://aceee.org/files/proceedings/2012/data/papers/0193-000024.pdf