by Burgerman » 19 Apr 2023, 19:22
What does matter is what voltage EACH INDIVIDUALLY drops to as you accelerate hard up an incline. That at least would tell you something! ut you need a fast voltmeter that remembers peak low, high etc.
Unloaded voltage tells you nothing useful. Unless you DISCONNECT the battery, wait 24 hours, and then it can give an approx state of charge. But it doesen tell you if its completely knackered or brand new healthy.
A completely knackered and completely discharged battery will read 13V or so after a short blip on a powerful charger. Its still dead, and still knackered!
A healthy fully charged battery will read 9v while crankin, recover to 12.5 to 12.7 after a heavy current like starting a car. But it still is 99% CHARGED and healthy. After 20 hours will read 13V. So which is correct? Neither, and both. Depending on impedance, peukert and battery recent history.