Help needed for newbie on How to use a foil assist

I am completely new to the foil assist world and looking at buying a secondhand homemade set up.
But only one battery
I am thinking sup foil only on a 7ft narrow board. But still paddle the board everywhere, but just blip the drive when going for a lump of swell. To reduce battery usage
Will this work, or am i missing the point of a foil drive?