Voltage testing can be useful if it's done under load specifically while the engine is cranking. A battery may measure 12V under no load but drop to 8 or 9 under starter load. I'd consider 10V the minimum.
Voltage should also be tested with the engine running at a fast idle. Minimum is 13.5V.
Voltage should also be tested with the engine running at a fast idle. Minimum is 13.5V.
