I can't run 2 stepper motors at the same time

Hi, I have a MicroBit Driver Expansion Board and I am trying to run 2 NEMA 8 Stepper motors (8HS11-0204S). I am using Makecode to program and the dual stepper mode to run it. It works when I run a single motor but I can't run both at the same time with the dual stepper mode. I am also using a 6 volt battery pack (4 batteries).