When I make golf cart cables or other battery cables I smear lots of rosin flux on the wire and inside the terminals before crimping. Then I heat the assembly and flow solder into the terminal until I'm sure that all the flux has been displaced and the area has no space that corrosion can occupy. I try to make the copper cable one with the terminal so to speak. Then I clean off any left over flux with a toothbrush and isopropyl alcohol. I have seen many connections that look good but are corroded inside. Checking for voltage drop or heating while heavy current flows will tell if the connections are good.