Battery Question

[Phrancus]

a quick glance would lead me to think of the other connections on the batteries. You connect the leads to either one but leave the rest in place? Then move the negative to the next position in the negative lead to that bus bar or beyond. But first of all, try it without anything else on the battery to eliminate that by actual experiment.

If I understand correctly, you have two sets of two batteries. within each set one battery can kill the other without you knowing it before the better of the two cannot keep the voltage high and also sinks into oblivion. 9V is definitely killing. Disconnect all, charge each to 13V, the one that drops within something like 15-30 minutes to less than 12 is no good. If they are classic ones that you can fill then that one will probably boil as well when you keep charging.

seems that the circuit works-ish with low amps but when more is drawn, it cannot deliver. So (didn't read back to see how you checked the batteries but if the CCA is too low it will show 12v but cannot perform under load) wire damage like the one you found earlier, remove and use a different one if available, or jump the leads one by one to find a fault in the line (as mentioned, can very well be under an isolating material, or corrosion within a terminal, a corroded bolt somewhere that spread its rust into connectors and such challenges to find.

[cjblovinlife]

Well !!! Thanks to everyone, I really did fix it this time. I removed all the ground wires that were stacked on the two engine blocks and created a bus bar inspecting every ground. When I flexed one of the wires it felt weak in the middle there was no visual corrosion on any leads but this one was completely corroded in the middle!!! I replaced it and everything works fantastic. It’s always a ground issue isn’t it?? Still not sure why it only showed up on the agnostic system but all fixed