It is possible and I have to admit, I have done it. But it is not recommended. It’s good practice to charge them separately or make another wire harness to connect the JST charge ports in parallel. I am actually selling both of my batteries. One is sold, and the other with the top-mount case, strap, wire harness, and the battery is for sale. LMK if you’d be interested! Pic below…
First of all, there is no BMS in the charge port. The BMS is inside the battery. To charge through the BMS, you need to charge through the little red plug (JST connector).
I only made a parallel harness for the output, not the charge.