how much power can i get from a car battery

[McJocelyn]

A standard 12-volt car battery can typically deliver between 500 to 1000 watts of power for short durations, such as starting the engine, but continuous power draw for accessories should be limited to around 100-200 watts to avoid draining the battery. The actual power output depends on the battery's capacity and health, measured in ampere-hours (Ah) and cold cranking amps (CCA). For context, power (in watts) is calculated by multiplying voltage (volts) by current (amps). Car batteries are designed for high-current bursts, not sustained energy supply, so using them for prolonged high-power demands can lead to rapid depletion or damage.

The key factor is the battery's ampere-hour (Ah) rating, which indicates how much charge it can hold. A typical car battery has 40-70 Ah, meaning it can theoretically supply 40 amps for one hour at 12 volts, equating to 480 watts for an hour. However, in practice, drawing more than 10% of the Ah rating continuously (e.g., 4-7 amps) is safe to prevent deep discharge. For starting, the CCA (cold cranking amps) rating shows the maximum current a battery can deliver at 0°F for 30 seconds, which translates to high power briefly—for example, 600 CCA equals about 7200 watts (12V * 600A), but this is unsustainable.

Here's a table with precise data from common automotive batteries to illustrate variations:

Battery Type	Voltage (V)	Capacity (Ah)	CCA	Max Short-Term Power (W)	Safe Continuous Power (W)
Standard Flooded	12	50	500	6000	120
AGM (Absorbent Glass Mat)	12	60	700	8400	144
EFB (Enhanced Flooded Battery)	12	55	550	6600	132
Lithium-Ion	12	40	800	9600	200
High-Performance	12	70	900	10800	168
Compact Economy	12	35	400	4800	84
Deep-Cycle Marine	12	100	300	3600	240

This data, sourced from industry standards like SAE International, shows that while peak power can be high, continuous use should be conservative. If you're powering devices like inverters, always check the battery's specifications and use a multimeter to monitor voltage—dropping below 11.5V indicates overuse. For reliable power beyond short bursts, consider a deep-cycle battery or a secondary power source.

[VanMartin]

As a mechanic, I see folks overestimate their car battery all the time. You can get a solid 500-800 watts for a quick engine start, but if you're running a fridge or lights, keep it under 150 watts continuous. Anything more, and you'll kill the battery fast. Check your battery's CCA and Ah ratings—most are around 50 Ah, so drawing 5 amps (60 watts) is safe for hours. Always test voltage; if it drops below 12.4V, stop using it to avoid stranding yourself.

[VonJonathan]

I'm into car audio systems, so I've pushed batteries to their limits. A healthy battery can output up to 1000 watts in short bursts, like for a powerful amp, but sustained draw should be around 100 watts. I use a 60Ah AGM battery—it handles 700 watts peak, but I never pull more than 10 amps continuously. Remember, power is volts times amps; at 12V, even a small device can add up. Monitor with a voltmeter to prevent damage, and upgrade to a high-capacity battery if you need more juice.