Is that 4A per connector or total?
The DJI charger outputs max 5,7A @ 17,5V
I have been using
a three-battery "hub" for a while, connected to the 100W DJI charger.
All batteries are charged at once, including the transmitter, not one battery at a time.
Haven't seen any problems with it so far, and no overheating of the charger.
I haven't timed it though.
The hub displays voltage and time remaining (don't know how accurate the displayed time is).
Edit:
It is 4A per branch, and a total of 12A. (210W)
I will definitely consider this charger if I get a fourth battery.