porous_grey_matter
Nominal battery voltages depend on the chemistry of the cell used, specifically the “oxidation potential” of the cathode and anode materials. You can think of it as “how badly one side of the battery wants to grab electrons from the other side”. 3.7 V is extremely common as it’s the number for common lithium materials. (But the real voltage varies a bit depending on the charge). Multiples of 1.5 V are common because it is the number for alkaline cells and you can get multiples of the voltage by putting several cells in series (end on end). I dont think there are commonly used chemistries with a nominal voltage of 2 V.
That probably captures many such things but it’s not fool proof. I like to make bread with 2-4 different kinds of flour, 4-8 different kinds of seeds, a teaspoon or two of sugar to get the yeast going, sometimes milk or olive oil or another fat source. At it’s most complex it could get pretty close to 20 ingredients but I don’t feel that should be classified as ultra-processed. The kinds of ingredients used and the actual process also matters.