[thingstodo]

The conductive grease that was mentioned by @WyrTwister, or something close to that, is what our electricians use to bolt together buss bars in electrical gear. The idea appears to be that even when it looks flat there are small variances in the surface of the copper. Torquing down the bolts tightly bends/squishes the soft copper and gets more surface contact. The grease is intended to fill the voids that are left and provide a path through the 'low' areas that would not normally carry any current.

It is applied with a razor-scraper type tool. Very thin, so that when the bolts are torqued the grease flows to the 'low' spots and fills the voids, but does not hold the 'high' spots apart.

It is tough to tell if it helps. The buss bar is between 3 and 6 inches wide, there are 4 bolts torquing down the connection. It does keep moisture out. And there is no obvious discoloration on the copper buss when you take the connection apart. But the grease has to be cleaned off so some surface discoloration may have been present.

EVTV advises to keep the battery connections clean and dry so that they can be checked ... one a year? Something like that. They also mention that high currents will expand the metal slightly then it contracts after cooling ... as a source for the bolts loosening off. They are big on nord-loc washers, that dig into the softer aluminum or copper and keep the bolts from working themselves loose. There is also a spring component to the washer that keeps pressure on the joint and allows for minute amounts of expansion and contraction without distorting the bolt.

I can't find the EVTV reference on Nord-loc. they have a couple of episodes where they talk about them. For the battery connections they have discussed 'clean and dry' many times.

I use Nord-locs on my battery pack, but it is not in a running car as yet - so no real experience to share. The thin layer of conductive grease makes sense to me, but again I have no testing of do versus don't to share.