If you are looking to be able to vary flow, you have a couple choices 1. Use a pole tap. 2. Use a controller
A tap will give you some variation of flow but the pump is now working flat out the whole time drawing 7 amps plus a n hour from the battery. Plus as the pump is trying to push 5 LPM into the hose that is then restricted by a tap you will have high pressure in the line as the pump is working against its self.
Using a control will also give you a variation of flow. The pump is now only producing the flow you need in turn you will be using 3 amps an hour from the battery have better flow as there is less resistance in the line. There are a number of controls on the market that would give you the flow variation and make teh system more efficient