how much current can a car battery supply

[MaryFitz]

A typical car battery can supply a very high amount of current for short bursts, but its capacity is limited. For starting a car, a healthy battery can deliver 250 to 600 amps for a few seconds. This initial burst is known as Cold Cranking Amps (CCA), a standard rating that measures the current a battery can deliver at 0°F (-18°C) for 30 seconds while maintaining a voltage above 7.2 volts. However, for sustained operations like powering accessories with the engine off, the safe continuous current is much lower, generally around 5-10 amps before risking a dead battery.

The key factor is the battery's purpose: it's designed for high-power, short-duration discharges to crank the engine, not for acting as a long-term power source. The exact current depends heavily on the battery's size, age, temperature, and its CCA rating, which you can find on the battery's label. Drawing high current for extended periods can cause severe damage.

Here’s a comparison of current supply capabilities for different scenarios:

Scenario	Typical Current Draw (Amps)	Duration	Key Consideration
Engine Cranking	250 - 600 A	3 - 10 seconds	Measured by the CCA rating; the battery's primary function.
Powering Headlights	10 - 15 A	30 - 60 minutes	Will significantly drain the battery; not recommended with engine off.
Running a Car Stereo	3 - 5 A	2 - 4 hours	Can drain the battery if the engine isn't running to recharge it.
Using a 12V Car Vacuum	8 - 12 A	20 - 40 minutes	High drain; best used while the engine is running.
Charging a Phone	1 - 2 A	Many hours	Minimal drain on a healthy battery.

Always check your specific battery's CCA and Reserve Capacity (RC) rating, which indicates how long it can supply a 25-amp load before dropping below a usable voltage. For any sustained power needs, it's safer to use the car's alternator (by running the engine) or a dedicated portable power station.

[ElliottLynn]

Think of it like this: it's a sprinter, not a marathon runner. When you turn the key, it can unleash a massive jolt of power—like 500 amps—for just a few seconds to get the engine turning. That's its main job. But if you sit there with the radio and lights on for an hour, you're asking it to run a marathon, and it'll just give out. For that kind of stuff, you're better off running the engine.

[LeHope]

The "how much" really has two answers. The burst current for starting is high, often over 400 amps. But the continuous current it can handle without damaging itself is surprisingly low, maybe 10 amps or so. A new battery might handle a bit more, but an older one will struggle. The big danger is trying to draw too much for too long; the battery can overheat, its plates can warp, and you'll permanently kill it. It's not a deep-cycle battery meant for that kind of use.