how low a voltage can a car start on

[Arya]

A typical gasoline car needs a minimum of around 12.4 volts to have a realistic chance of starting. However, at this voltage, the battery is only about 75% charged and is already considered weak. For a reliable start, especially in cold weather, you want to see 12.6 volts or higher. Once voltage drops below 12.0 volts, the battery is effectively discharged, and starting the engine becomes highly unlikely.

The key factor is cold cranking amps (CCA), which is the current the battery can deliver at 0°F (-18°C) for 30 seconds while maintaining a voltage above 7.2 volts. Even if the open-circuit voltage seems okay, a battery's ability to sustain voltage under the heavy load of the starter motor is what matters. A weak battery might show 12.2 volts but then immediately plummet to 8-9 volts when you turn the key, which is insufficient for the starter.

Here's a quick reference for battery voltage and its state:

Battery Voltage (Resting, Engine Off)	State of Charge	Likelihood of Starting
12.6V - 12.8V	100%	Excellent
12.4V - 12.5V	75% - 85%	Fair (may struggle in cold weather)
12.2V - 12.3V	60% - 75%	Poor (risk of not starting)
12.0V - 12.1V	40% - 60%	Very Unlikely
Below 12.0V	Discharged	No

If your battery is consistently low, the issue might not be the battery itself. A faulty alternator that isn't properly recharging the battery, or parasitic drain from a component that doesn't shut off, are common culprits. Using a multimeter to check the voltage is a simple first step. If you get a reading below 12.4 volts, it's a clear sign your battery needs attention, either from a recharge or a replacement.

[SanJack]

If your multimeter reads below 12.4 volts, you're on borrowed time. That battery is weak. At 12.0 volts, it's pretty much a paperweight for starting your car. The real test is what happens when you turn the key—if the voltage drastically drops and the starter sounds slow and labored, the battery is the problem. Get it tested or charge it up. Don't just wait for it to fail completely.

[SerenityFitz]

I learned this the hard way last winter. My car showed 12.2 volts in the morning, and it just went "click-click-click" when I tried to start it. The mechanic explained that the voltage might look okay, but the battery didn't have the strength (those cold cranking amps) to actually turn the engine over in the cold. Now, if I see it dip below 12.4, I take it as a warning to take a longer drive to recharge it or get the battery checked.

[Moore]

Think of it like this: the resting voltage is the battery's potential energy. The real question is, can it deliver that energy under load? A healthy battery should stay above 10.5 volts while cranking. If it drops below 9.6 volts, the engine control unit might not even get enough power to function, preventing the start altogether. So, while 12.4 volts is the minimum resting voltage for a chance, the critical test is the voltage during the starting process itself.