One Apex 300 can connect to up to 6×B300K/B300S/B300 batteries.
You can also mix different battery types (B300, B300K, and B300S), with a total of up to 6 batteries.
If your B300K is using the short cable, connect that one first, as the short cable should be closest to the Apex 300.
Check the step-by-step guide to help you get set up quickly and easily.