So here's a dumb electrical question

Again, you cannot go by physical area. You must go by ampacity. One problem of course is that all charts are not equal LOL

Here for example:

https://www.bluesea.com/resources/1437

This chart

http://assets.bluesea.com/files/resources/newsletter/images/DC_wire_selection_chartlg.jpg

In the 20ft "critical" column, this would suggest that no 0 is good for 150A

In the same 20ft column, 12 ga is "not shown" but borderline at 10A. This would suggest that FIFTEEN 12ga wires are needed to equal no0

Other factors you must consider is strand size. In AC especially higher frequencies, you get into "skin effect" which requires larger conductor size. DC does not suffer this, but battery cable typically has larger strand size, which would surely negate any physical comparison

I didn't bother to check, the distances in that chart are likely for two wires, as this was from a marine oriented site.