This method is for the battery cables that attach via a bolt or a stud and a nut. The use of copper tubing here is much more effective as the pre made ends cost probably 100x more than what you can make these for.
So the first thing you'll want to do is cut a piece off that is going to make your new end. I am using 3/8 OD copper tube that I picked up from Home Depot. It's meant for refrigerator coolant lines.
The wire I am using is welding cable, I got some in 4 gauge and in 2 gauge. The 4 gauge fits in this perfectly. The 2 gauge I had to flare out a bit, but once flared it's easy to get all of the wires in.
Just tap it lightly onto the swage. Being soft copper it won't take much force. This here was enough to get everything fit.
You can see how the 2 gauge wire will now go in with ease. You might have the one off strand sticking out but it's easy enough to get them back in there if you pay attention.
Then you want to strip the insulation back a bit longer than the new end fitting. This is so the wire can actually stick out the other end. Hit it with a bit of flux.
The flux will help keep the thin wires pasted together when you insert them into the fitting. Like so.
Then comes the hammer. Smash a good bit of the end. You want enough flat that there is ample room for the hole and enough clearance for any washers and bolt heads that will be installed.
Now to solder the connection. I like to heat the end and flow the solder in from the other side of the fitting. It will wick it's way through any voids and come out the other end.
And here it is soldered. It'll get prettier.
Drill the appropriately sized hole through. I recommend center punching the terminal end so you stay on track with the bit.
Here we are all drilled out.
I then shaped the end a bit on the belt sander, nothing too fancy. If you want to take the time to smooth it all out and polish it shiny, go for it.
Then apply heat shrink tubing. Some people don't like the heat shrink on their battery leads. I'm not one of those people. Also this helps smush the dielectric grease into any voids in the wire at the connection.
And done. Now it's just a matter of repeating this as needed for however many connections and cables you need.
And just in case anyone wonders about voids from it not being properly crimped, here are some cross sections
Since I'm doing this for my 90 civic wagon I figured I would show the cables I cut just so there are some numbers to reference for length.
Also I ran out of heat shrink for one end but I'll sort that tomorrow.