A typical car battery can supply between 600 and 1200 watts for a short period, but this is highly dependent on the battery's health, age, and temperature. The key factor is the battery's Cold Cranking Amps (CCA), a rating that measures its ability to start an engine in cold weather. To calculate the theoretical wattage, you multiply the battery's voltage (12.6V when fully charged) by its Amp-hour (Ah) rating, which is typically 45Ah to 70Ah for a standard sedan. This gives a total energy capacity of roughly 567 to 882 watt-hours. However, this is a measure of total stored energy, not instantaneous power.
The more critical number for understanding what you can run is the RC (Reserve Capacity). This is the number of minutes a battery can supply 25 amps of current before its voltage drops too low. At 25 amps on a 12V system, that's 300 watts.
| Battery Type | Typical Ah Rating | Approximate Watt-Hour Capacity (12.6V) | Common CCA Rating | Theoretical Max Sustained Wattage (for ~10 mins) |
|---|
| Standard Sedan (Group 48) | 70 Ah | 882 Wh | 600 CCA | 300-400W |
| Large SUV/Truck (Group 65) | 85 Ah | 1071 Wh | 750 CCA | 400-500W |
| Performance Car (AGM) | 70 Ah | 882 Wh | 700 CCA | 350-450W |
| Compact Car (Group 35) | 45 Ah | 567 Wh | 450 CCA | 250-300W |
It's crucial to understand that drawing high wattage for more than a few minutes without the engine running will quickly drain the battery. For example, using a 500-watt inverter to power tools or a small TV can deplete a standard battery in under an hour, potentially leaving you stranded. The battery's primary job is to start the car; using it for high-demand accessories should be done sparingly and with the engine running to allow the alternator to replenish the charge. For regular high-power needs, a dedicated deep-cycle battery is a much better solution.
