POWER DROP OFF

We are running our AX3500 driving 1 motor each side. The motors are wired to 24vdc. All indication is they are working fine. Our Battery Voltage reads 24.588 and Internal Voltage reads 11.886 from the AX3500. When we drive the motors at full AX3500 speed (127) the AX3500 reports 127 commanded until the Battery Voltage reaches 21.668 and then the AX3500 report 3Fx0 vice 7Fx0. Basically when the voltage reaches 21.668 the controller halfs the power provided to the motors.

Any idea?

Thanks,
Marshall