Let's assume an average iPhone battery is 5.45Wh and that they are charged to full every other night. That is 0.99kWh/year. We know there are 136 million iPhone users in the USA (1) so we are looking at 134GWh of electric consumption shifted to green generation.

Now assuming those phones were previously charged on the standard energy mix in the USA that is 0.368kg of co2 saved per device per year, or 501,584,76kg of co2 saved. That seems like a huge number! But is it?

Well let's put it in perspective. A flight from Heathrow to New York emits 312kg of co2 per passenger (3) so we have saved the equivalent of 600 fully loaded transatlantic flights. There are ~1700 flights a day so it doesn't seem like a huge difference. Disappointing.

But it seems like a pretty easy win so at this point I ask why not do it? I'm a big believer in aggregation of marginal gains and there are 10x that number of iPhones worldwide and many more Androids.

(1) https://www.bankmycell.com/blog/number-of-iphone-users (2) https://carbonfund.org/calculation-methods/#:~:text=We%20cal...). (3) https://www.nesta.org.uk/press-release/gas-boiler-emits-more.... (4) https://www.eurocontrol.int/news/celebrating-100-years-trans...