The voltage is varying as the lipo charges so the charger may continue to reduce charge current to stay under its 50watt limit. There should be some current variation as the voltage increases thru the charge. This is what a 50watt charger does that allows them to advertise it will charge 6S lipos. It will to, just takes a while.

The voltage was 50/3.22 = 15.53v when you saw the 3.22a charge rate.


You'll need a 100watt charger to charge at full 1C charge rates with a 4S lipo.