I needed 4 AWG cable to lower wire resistance over the distance required. 6 AWG wire was not large enough. Also didn't want to use a larger Anderson plug as that created a list of new problems.

So I expanded the lug:

I drilled a block of wood to the right depth to support the end of the lug & the bottom of the cup. With a bit of grease I first used a Dynabolt which was 6mm at the end & hammered that in. That worked really well & I could wiggle it back out. The next stage was more difficult as I couldn't wiggle the punches out.

Using progressively larger (old) drill bits, I filed a small taper on the back, only needs to be larger by the diameter of the previous size, so 0.2mm at most, & hammered in. It is better progressively work down the cup with larger sizes. Do not try to go all the way down with one size then all the way down with the next larger size as that is more difficult to get that punch (drill bit) out because you don't have wiggle room so to speak.

I did have to drill a hole in the piece of metal (make the hole a bit loose) to make a tee handle & put that over the drill bit & then drill bit backwards in a drill to clamp the drill bit, to be able pull the lug off the back end to the drill bit a few times.

Cleaned off the grease & the lugs looked in pretty good shape. Wouldn't want to do this all the time but for the odd 4AWG cable is wasn't too difficult & didn't have to buy any extra tools. Buy a Dynabolt (back end 6mm) if you don't have one, as it would be the worth getting for the first enlargement as the was easy.