Question on connecting 6 volt batteries in series for 12v?

Jades

It's been a little while since I've worked on my van. I connected the batteries in parallel, such that I had 8 cells connected to make 12 volts.

I'm not sure why I connected the two 6v packs the long way (1st terminal negative on 1st battery to 1st terminal positive on second battery vs 4th terminal negative on 1st battery to 1st terminal positive on 2nd battery). Shouldn't it be that second option? (And if that is the case, should I just drill out copper bars (or other metal?) to connect the two 6v packs? Else Explorist on youtube use 4/0 wire.