OK, first of all, I am not trying to be a jerk.
I am honestly just trying to help you out here.
The batteries in question are indeed batteries in question.
Brand new to the vaping world and no street creds yet.
Me, I will not purchase ANY battery until it has been tested and blessed by the Flashlight Folk.
Possibly the only folks in the universe as we know it that are as serious about batteries as we are.
And they know their shit.
IMHO, there are three reasons they are not charging.
First of all, the charger you have. But NItecore makes AWESOME stuff so I am not worried about the charger.
Secondly, the batteries, a brand that I am not familiar with are crap. No matter what the dude behind the counter tells you.
And to be honest, I have never gone to a brick and mortar vape shop where they only carry one brand of battery.
"Danger Will Robinson" if you are old enough to remember that.
The last thing may be that these new "Wonder Batteries" are slightly shorter than the well known brands that work.
Two options for you.
Very Gently bend the the tab of the sliding part of the connector of the charger toward the top to make better contact with the battery.
Even better, go to your local hardware store and purchase some very small steel washers and put one of them at the negative end.
A very small magnet would be better.
Lastly, you can pick up Samsung 25R, 2500 mAh batts that are rated for 20 amp constant for $8 or less!
Dat's all I got and I hope it helps!