Hiya,
I’m having trouble with this - I want the opacity of text to reflect the remaining amount, to a minimum of 3% or so. Advice much appreciated.
You can do that using the battery formula in either the Layer Visibility or your Item Paint field. You will have to first click the check box at the right side of the Paint field or the Layer Visibility and then press the calculator icon near the top right corner of the screen to convert it to a formula field entry.