Ekavir High-Capacity 18650 Li-ion Battery: 2600mAh, 3.7V with Wired

The batteries arrived within nominal voltage - 3.98V. Using my 18650 charger, never completed the charge and battery reached 4.04V - odd. No matter what I did, the battery never reaches 4.2V. (I am using a fairly sophisticated charger.)Now, the big issue: The battery voltage drops below nominal voltage when drawing anything above 100mA current. Using a variable load circuit, I could see that below 100mA, the battery would supply 4V and slowly discharge, but the moment I increased load, it would drop below 2.4V. Reducing the load back below 100mA again brought the voltage up.Then I tried manually charging using my bench power supply. It still never reached 4.2V - it would stop drawing current at 4.04V of the battery.I am an enthusiast and not an expert, hence don’t know what exactly is the problem. But both batteries I bought, behave like this.My hunch is that these are used / refurbished batteries. But I may be wrong and don’t take my word.