Can a car battery show fully charged and still be bad?
If the battery cannot reach higher than 10.5 volts when being charged, then the battery has a dead cell. If the battery is fully charged (according to the battery charger) but the voltage is 12.5 or less, the battery is sulfated. If your battery cannot even reach a full charge, consider it bad.
How does the car battery charger know when the battery is dead?
So the battery charger doesn’t really know when your battery is charged it just knows when current is no longer leaving the charger.
Is it possible to read the terminal voltage of a dead battery?
It’s possible to read nearly the fully rated terminal voltage on a dead cell if you take a no-load measurement. This is due to the battery’s internal resistance and the loading effect of the measuring device (the theory behind this is complicated and I won’t attempt to get into it here).
What does 12 VDC mean on car battery?
Put the leads where the cables connect on the battery. Red on the + (positive) and black on the – (negative). It will read 12 VDC when the battery is charged and the engine is off. What could this possibly mean?
What does it mean when a car battery is not charged?
The battery is shot. The charger indicating a fully charged battery means one of two things: the battery is fully charged, or the battery is faulty and won’t take a charge. A battery that has sat for a month and then expended some energy trying to start the engine is not going to be fully charged.
So the battery charger doesn’t really know when your battery is charged it just knows when current is no longer leaving the charger.
It’s possible to read nearly the fully rated terminal voltage on a dead cell if you take a no-load measurement. This is due to the battery’s internal resistance and the loading effect of the measuring device (the theory behind this is complicated and I won’t attempt to get into it here).
What should I do if my car battery is dead?
Now connect the black cable clamp to the working battery’s negative (-) battery terminal. Do not connect the final black cable clamp to the dead battery. Instead, attach that clamp to an unpainted, metal part of the car, such as a clean nut on the engine block. This will help ensure a safe jump.
Put the leads where the cables connect on the battery. Red on the + (positive) and black on the – (negative). It will read 12 VDC when the battery is charged and the engine is off. What could this possibly mean?