There are a couple of problematic connections in my battery layout. Particularly, the connection between A4 and A5 in this diagram is tricky. I tried making a traditional cable, but the 4/0 cable I'm using does not flex enough. So, I improvised. Looking up the specs on welding cable, I found that three 2 gauge cables are nearly identical to one 4/0 gauge cable, both in circular area as well as specified ampacity. So, I cut and stripped three lengths of 2-gauge cable (here shown next to 4/0 gauge lugs):
I firmly taped the three together, then fit 4/0 lugs onto them...
...then crimped the snot out of them (after all, who wants snotty cables?):
Here is the crimped flexi-cable:
And here is me flexing it one-handed. I could not come close to flexing the 4/0 gauge cable like this:
I double-heat-shrink-wrapped the ends:
And here it is, snug in its location: