OK good. 12.55 is close enough. It could still be bad because they show 12.6 at static (no load) then break down under the extreme load of starter.
Yes, I was speaking of 55.1 55.2 trucks. Wanted to look at the correct schematic in case there were changes. If a car motor has something different than what I said, I don't know it.
I still say battery or wires/cables/terminals/clamps/connections/corrosion/, lead/copper sulfate.... The jump from another battery is still necessary. A helper is not mandatory. Pull other vehicle close, hook up cables and start motor. Stop motor, get out and disconnect. The posts and clamps MUST be thoroughly cleaned. The idea is to see if starter suddenly acts normal whether it starts the motor or not.
You can also take the battery to two different places. They will put under load and test. Don't trust one place/machine/operator. O'Reilly's, Autozone, etc do it for free. In or out of the vehicle.
So many times I have seen myself and others struggle when it was the battery or it's connections. It will fool you. So we must be 100% sure before blaming something else. This includes battery ground to the motor, ground to body and frame.
