Using a Watts Up Pro Electricity Consumption Meter, oPower discovered that it takes about 10.5 watt-hours of electricity to fully charge an iPhone 6. If you do that 365 times a year, that's 3.8 kilowatt-hours in total. At an average US retail price of 12.29 cents per kilowatt-hour, it will cost iPhone 6 users just $0.47 per year to charge their device.
The iPhone 6 Plus has a larger battery and thus draws more electricity per fill-up (16.8 watt-hours). However, oPower estimates that it only needs a fill-up once every 1.46 days. Thus, it will cost iPhone 6 Plus owners about $0.52 per year to charge their device.
These numbers are slightly higher than the $0.41 it cost to charge the iPhone 5 annually; however, the new generation devices have significantly larger screens and thus demand more energy.
Read More [via Heder]