Like the alternator mounting points, all the heavy terminals should be cleaned & coated with electrical grease. I found this junkyard cable, cut its orange fusible link at the battery terminal, and then crimped & soldered a new ring onto it for the battery end. With these new batteries, I also converted to stainless studs & nuts, so it will be easy to attach this cable. Another option would be an aftermarket bolt with an extra bolt or stud for extras, like this alternator. Here's a clickable example, but I don't sell or endorse any:

The voltage regulator pigtail (center) must be spliced into the original alternator's Brown wire, and I highly recommend a pierce splice as shown in this image:

The worst way to splice it would be a ScotchLok, because it would compromise BOTH alternators.