A standard 12-volt car battery can produce a maximum power output of approximately 1,440 watts for a very short period, typically during engine cranking. This is calculated using the formula: Power (Watts) = Voltage (Volts) x Current (Amps). For a battery with a common Cold Cranking Amps (CCA) rating of 120A, the calculation is 12V x 120A = 1,440W. However, this is a peak, unsustainable load. For continuous use, like powering devices through an inverter, a safe maximum is much lower, generally around 120-180 watts to avoid damaging the battery.
The actual wattage depends heavily on the battery's key specifications. Cold Cranking Amps (CCA) measures the maximum current a battery can deliver at 0°F (-18°C) for 30 seconds while maintaining a voltage above 7.2 volts. This is crucial for starting your car. Amp-Hour (Ah) rating, often found on deep-cycle batteries, indicates the battery's energy storage capacity, telling you how long it can deliver a specific current.
| Battery Type | Common CCA Rating | Peak Power (Watts) for 30 sec | Common Ah Rating | Continuous Safe Power (Watts for 1 hour)* |
|---|
| Standard Sedan Battery | 500 A | 6,000 W | 45 Ah | ~540 W |
| SUV/Truck Battery | 750 A | 9,000 W | 70 Ah | ~840 W |
| High-Performance AGM | 900 A | 10,800 W | 80 Ah | ~960 W |
| Marine Deep Cycle | 150 A (MCA**) | 1,800 W | 100 Ah | ~1,200 W |
| *Calculation: (Ah x 12V) x 0.5 (50% Depth of Discharge safety buffer). *MCA is measured at 32°F (0°C). | | | | |
For continuous power, it's critical to not drain the battery below 50% of its capacity. Using a 100Ah deep-cycle battery as an example, you have about 600 watt-hours of usable energy (100Ah x 12V x 0.5). This means you could theoretically run a 100-watt device for about 6 hours. Always connect high-wattage accessories directly to the battery terminals with appropriate fuses and use an inverter rated for your power needs.
