I'm not familiar with other suppliers mentioned here, but we buy from Waytek often for our battery lug supplies: https://www.waytekwire.com/products/1424/Battery-Lugs/&pageSize=36 They have about every kind of lug imaginable and they're well marked for proper sizing. I'd also recommend one of those hand-held hydraulic crimpers. Much easier to control the crimp on bigger lugs & you get a nicer crimp, I think. As others suggest, consider using colored HD heat shrink (it's THICK!) over your new connection when finished. Of course, you have to slip the heat shrink on the cable before crimping. | 
What is needed to gear up to make battery cables?
