Here are some rough numbers. The unit has 32 lbs force of thrust. This is pretty close to 1/4 hp. 0.25 hp x 0.746 = 0.186 kw = 186 watts, slightly less power than two 100 watt light bulbs.
P = IV I=P/V. Let’s use 36 V for the unit.
The amperage of the motor would be 186 watts/36 V = 5.1 Amps
Since the battery is rated at 4 amp hrs the max run time at full speed is 4/5.1= .78 hrs = 47 minutes.
If this was a 12 V unit with 32 lbs thrust with a 60 amp hour battery, the amperage would have to be 186 watts/ 12 V = 15.5 amps. 60 amp hr/ 15.5 amps = 3.87 hrs.
The large battery would last almost 4 hours.