I expect the honest answer.

I cut jumper cables down so that they can connected to battery terminals and deliver the necessary amperage. I have a super capacitor bank (got it pre tarrifs)

Honestly?
I'm willing to help you out if you want.
It's not good. I would dare say it's possibly even a hazard as it is.

The key to soldering is to heat both of the parts that you want joined, then apply solder to that.
Baeically, you mostly don't melt the solder with your soldering iron, the heated joint melts the soldering.

What you got here looks like a cold solder, which is basically melted solder applied to cold metal.
It makes a weak connection that will fail or even come apart.

Start by making a good solid mechanically strong splice that maximizes contact area.
Starting from 2 clean stripped wires, join them together in sort of a X shape.
At the same time, twist each wire clockwise around the other.
(Like cross both wires in a x shape, holding each half between your index and thumbs, twist in opposite directions, one thumb away, one thumb towards you.
Twist as tight as you can. Bigger gauge stuff like what I think you're working with might need pliers.
Once that's done it's already a strong connection even before solder. )

Then to solder, heat the whole splice.
Say you're heating the top of the splice with your iron, apply solder from the bottom.
It's the heat from the wires that should melt the solder not your iron.

I don't know how to explain better, maybe pictures or videos.
Don't give up.

Awesome an admin said my solder job is ass.

I think I get it. The wires will be woven together and twisted. Sounds like that would make a bend, but anything For a Better solder job.

I did Rush because wire will pull heat down into the Cables.

Maybe I could have hit it with the heat fun more and maybe I apply heat before I put on the Flux

It's a very bad job. Just being honest. The solder didn't get hot enough and the wires weren't joined properly prior to soldering. The solder should "flow" into the wires not glue them together.

I think this wire is a bit difficult to solder because it's very thick, with a normal soldering iron it might pull away too much heat for the two wires to get to temperature

It's normal for the wire to get hot while soldering though, and it's fine to an extent. Just don't hold them with your hands :)

If you're having difficulties, it might be better to "tin" each of the wires before soldering. It makes it a lot easier in terms of holding the wires in place

I'll add more heat next time

I give it a "what year did your house burn down" out of ten.

You see the upper left portion of the black wires' solder connection where the solder has flowed into the wire and it looks like matted down hair? That's how it all should look. More heat will definitely help.

Luckily they won't get used much. They'll be used to jump cars which it successfully did

I'm hoping that it's what it looks like internally. Also I can't pull apart the soldered joint