You can't charge such batteries via their +/- terminals. These must be charged through micro USB port on the side. This is confirmed on Q&A of the product page.
Basically these are casual 3.7V Li-Ion chemistry inside with some step-down DC-DC module built-in. And a charger circuit which actually charges them from 5V USB as a casual Li-Ion cell charger.
Due to this their discharge curve are pretty flat. You'll get almost constant 1.5V until a Li-Ion actual cell voltage drops to somewhere around 3V where internal protection circuit just cut if off and you'll get 0V output. So you can't charge it with such chargers as it won't drop below 1.5V like normal NiCD/NiMH cells do. Even if you apply higher voltage on +/- terminals basically you'll apply it to DC-DC output.