1000w output motor@ maximum 90% efficiency will draw a minimum of (1000w / .90 = 1111w / 48V = 23.14A)
1000 W 48 V ebike motor can draw 48V >23.14A motor input to produce 1000w motor output.
48 V 10 ah lithium battery is rated for "≤12A", and likely fused, for a "maximum" 15A max output.
Nothing wrong or bad about the battery ...
Motor too big for the battery or battery too small for the motor.

You could up the fuse in the battery but only at the risk of its destruction and the certainty of its greatly reduced lifespan.