Running a 12V toy car on 18V using 5 18650 cells

Ryobi powertool pack with 5 18650 high discharge cells (30A). No BMS was used so the motors get as much current as they want :). This thing spins tires now. Since the cells are only around 2Ah the full throttle fun was over in 15 minutes :(. I will have to add another pack or two in parallel to extend the play time.