Hi Ritchie. A lot will depend on the AH (amp hour) rating of the battery, Current drawn and the number of hours worked.
EG setting the flow controller around 50 - 60 flow rate, the pump will draw 3 - 4 amps per hour. times this by the time worked to give you the approx amps used.
Battery manufacturers recommend the battery should not be depleted by more than 50% of its capacity or for volts to fall below 10.5v
So if you have a 80AH battery, you can drain 40 amps in theory before you need to charge the battery. Bear in mind the lower the amps the longer it will take to recharge. Also as the battery nears full charge it will take less amps from the charger.
Based on my example of 3 - 4 amps and hour used an 80AH battery could give you 10 hours work before it needs recharging.
A better guide is the volts shown on the controller at the start of the day I would suggest volts should be 12.5 or more.