I checked out my charger for my cell phone. It says 7 watts max. So I assume 3 watts standby would be realistic being its a switcher type and not transformer type. So given I pay about 12 cents a KWh
1000/3 = 333.3 Hours per Kw consumed.
$10/.12 = 83.3 KWh for $10
83.3 x 333.3 = 27775 hours for my ten dollars.
So for me a few tens of thousands of hours seem pretty realistic.
And factoring in there are 8765 hours in a year.
That would mean I could leave it plugged in for about 3.16 years.
Or leave it accidentally plugged in on occasion for around 200 years of twice a week oops I forgots!
You may seriously want to look at your clock radios though. all of mine are rated at 12 -15 watts! And the run 24/7/365!
I am not trying to be a jerk but I do tend to play the devils accountant whenever I can with the environmentalists!
I have yet to find any numbers the enviro nuts toss around to be even remotely true let alone even loosely based on real facts. I find someone else's ignorance, foolishness or misguided logic to be no reason for me to change my ways. Prove the reasons scientifically and accurately with repeatable and provable evidence and I will happily change my ways!
I believe that being environmentally conscientious is a good thing but I prefer to go after the bigger issues. Cell phone charger efficiency is nothing compared to what your home heating and cooling systems use or your essential convenience items in general.
And I have reduced my home power usage by nearly half in one year by dumping some inefficient big power use items!