The L298 driver can't handle the current required by your low voltage, high current stepper. It will overheat and shut down. There are a couple of other options. The first is to put a resistor (e.g. 6 ohms, 10 or more watts) in series with each winding to reduce the current, which wastes power. The other is to use a modern stepper driver like the A4988 or DRV8825 from Pololu Pololu - DRV8825 Stepper Motor Driver Carrier, High Current
With the latter option, you still need to cool the motor driver to get the full current through the motors. However you can reduce the motor current to a reasonable level (for the motor driver) using the on-board adjustment.
Finally, if you discharge the LiPo batteries much below 2.5 V/cell, they will be destroyed. You will need a battery protection PCB to avoid that. See Tenergy Battery Pack PCB