That is usually caused by an old, worn out, or faulty battery pack. We would test the Voltage of the battery pack with the cart on the ground while being sat on or held still, with the power switch on, and the accelerator in the full throttle position. If the Voltage drops under 23 Volts during this test then the battery pack is bad and needs to be replaced.
If the battery pack Voltage stays above 23 Volts during this test please let us know and we can take it from there.
Cari Kruzel-Boxwell