Unexpected result when charging cell phone

I want to run a confusing occurrence by somebody here, in case I am overlooking something. Basically, it looks like charging a cell phone using an extension cord is affecting the battery, although I don't think this is possible.


The full story:
I have a cell phone with its original charger and lithium-ion battery, and also a 3rd party lithium-ion battery. After two years of usage, both batteries still held their charge well. I have been charging it from the same outlet (Outlet A) for the past two years ... but then I decided to use a different outlet, and problems ensued.

Here is where this gets puzzling. For many years, the in-accessible outlet behind my desk (Outlet B) has only powered a desk lamp, which has always worked well. Several months ago, I plugged in an old extension cord to this outlet, and ran the cord to an easily-accessible spot on my desk, where I began charging my phone. What is ODD is that after fully charging my cell phone through the extension cord, the battery life dropped noticeably - the total run time (talk time) between charges dropped to half of what it was prior, and also, the cell phone began to shut off while at "two bars" on the battery meter, as opposed to one bar. I figured the battery was the culprit, but after swapping batteries and charging from the same source, the phone gave the same performance.

After a few months, I figured I would try charging from the outlet I used prior (back to Outlet A), and the phone's run time and performance have improved - it now runs for approximately the same talk time, and the phone never cuts out abruptly when the battery meter has two bars of strength.


So, sure, I could take the extension cord to a different outlet and compare results, but from what I know, this should not affect the quality of the charge. Is the extension cord affecting the battery's charge?

Thanks in advance for your responses!

 

This is occurring in Ontario, Canada. The outlets supply 120 volts.

The outlet has ground, but the extension cord is two-prong. The cell phone charger is also a two-prong charger.