I think you are incorrect on this as typed, there is a difference between non restricted flow and restricted flow through the a.i. tips. The .50 tips flow .42 gpm @ 20 psi and .73 gpm @ 60 psi , hence the higher pressure will flow more gpm.Thanks RS. Here is a link. More pressure results in less flow per minute. And greater amperage draw from the battery.
Are you using 4 nozzles? If so, your flow would be 2 gals per min.
Put the charger on your battery overnight to see if that helps.