Here's the other half of this problem. The first half was caused by improper torquing of the nyloc nut with pliers. Please DO NOT use pliers to tighten and torque battery terminals!!


The second problem arose because the person who connected these batteries left the flat SS washer on top of the battery post. This means it was sandwiched between the lug and the lead of the battery post. Stainless steel is a HORRIBLE conductor, one of the worst.


In battery installations flat washers should never be placed between the lug and battery post only ever on top of the lug.


I quote the relevant ABYC standards from E-10 Storage Batteries here:


10.8.3 Battery cables and other conductors size 6 AWG (13.3 mm˛) and larger shall not be connected to the battery with wing nuts.


10.8.4 Multiple conductors connected to a battery shall be installed with the highest ampacity conductor terminal closest to the battery, followed by successively smaller ampacity conductor terminals.


10.8.4.1 A maximum of four conductor terminals shall be permitted to be installed on a single battery stud.


10.8.5 Flat washers, if used, shall only be installed immediately under the split lock washer and nut of the attachment stud.