How do I determine the run time of a battery operated machine?

Use this formula based on the information on the battery and machine to use:

Battery intensity (in Ah) x Battery Voltage (in V) / Machine Power (in W) = Opertating Time in minutes. Thus a 5Amp/ 40V Battery used on a 750 Watt machine will last +-26 minutes. 5Amp x40/750= 26.6 (Intensity of the job dependant)