No doubt, hardness can vary with whatever mix of various different types of connectors. The batch of battery terms I got measured 15 BHN with the Lee hardness tester (measured boolits that were aged a few months).
Years back, when I pondered buying 3 pails full (5 gallon size) of battery terminals from the local auto-recycler for 30¢ per lb ...Ian told me to not hesitate buying them (he used different words
)...also, I did make out pretty well, when I sold the copper/brass leftovers from the smelt.
Today, I'd hesitate to buy them. Many of them had plastic insulation that was extremely difficult to remove before heating them to alloy melt temp. So you end up melting some plastic (burning on the melt). It's a stinky, messy endeavor, and I live in town (single family dwelling with average size lot) with close neighbors. Other alloys are available to me, so I'll pass on that work/mess. If there weren't other alloys readily available at a fair price, then yes, I'd buy and process battery terms.
That's mt 2¢