A typical car needs around 12.6 volts when the engine is off to start reliably. However, the critical factor is what happens when you turn the key: the battery must supply a minimum of approximately 9.6 volts while cranking the engine. If the voltage drops below this threshold under load, the starter motor won't have enough power to turn the engine over, and you'll likely just hear a clicking sound.
This 12-volt standard is the foundation for most gasoline-powered passenger vehicles. The battery's resting voltage (when the car is off) should be between 12.4 and 12.7 volts for a healthy charge. When you engage the starter, it places a massive load on the battery, causing the voltage to drop. This "cranking voltage" is the real test. A battery that shows 12 volts but plummets to 8 volts under load is failing.
Here’s a quick reference table for what your voltage readings mean:
| Condition | Voltage Reading | What It Means |
|---|
| Engine Off, Fully Charged | 12.6V - 12.8V | Battery is in ideal condition. |
| Engine Off, Needs Charge | 12.0V - 12.4V | Battery is partially discharged; may struggle to start. |
| Engine Off, Discharged | Below 12.0V | Battery is critically low; likely won't start the car. |
| While Cranking (Key Turned) | Above 9.6V | Battery and starter are functioning correctly. |
| While Cranking (Key Turned) | Below 9.6V | Battery is weak or failing, or there's a bad connection. |
| Engine Running (Charging) | 13.7V - 14.7V | Alternator is working properly to recharge the battery. |
If your car won't start, using a multimeter to check these voltages is the first step. A low resting voltage means the battery needs a charge. A good resting voltage but a low cranking voltage points to a dying battery. If both voltages are good but the car still won't start, the issue could be with the starter motor, ignition system, or fuel delivery.
