There is now a new estimate that keeping an iPhone 5 charged over an entire year will consume 3.5 kWh. Other phones with different battery capacities, however, may incur substantially different charges. For example, Samsung's Galaxy S III manages 4.9 kWh. By itself, a single smartphone will cost less than $1 over an entire year to charge. For this writer, the cost is about 31 cents.
However, in aggregate, the power consumption of all smartphones is substantial. Opower said that the 170 million iPhones that are expected to be sold over the next year will consume as much power as all homes in Cedar Rapids, Iowa, which has a population of 128,000 people. Of course, the company also noted that the local battery is not the only power concern in a smartphone, but the data centers delivering information to those phones need to be considered as well. On the positive side, we are using smartphones for tasks we previously used notebooks or desktop PCs for, so we may end up with a power reduction after all.
Opower noted that a typical desktop PC requires about $28 of power per year to run, while a notebook needs about $8.