x2 @ 1/2 full of hot solder and hot cable
I've done tons of them, you need
1) some heat shrink tubing
2) a basic small torch
3) some pliers or vise grips to hold the lug up vertically
4) a hammer
5) the right solder.
Put some heat shrink tube a ways up the sleeve of the cable and expose 1\2" of bare cable.
Heat the lug and push the solder in to it until it melts easily.
Continue to apply flame and s l o w l y plunge the bare copper down in to the solder until you can't go more and the solder overflows and leave in place for 10 seconds. Remove the flame.
Turn off the torch, lay the lug horizontally on to the concrete or some really solid surface and whack the back of the lug with the hammer once while it's still very hot. There's your solder, and there's your mechanical grip.
Push the heat shrink tube down to the joint covering the seam and heat and shrink it. If you want to be savvy use red and black cables and heat shrink tube.