Most standard car batteries have a capacity between 45 and 65 amp-hours (Ah). This rating, often found on the battery's label, indicates how much current the battery can supply over a specific period. For example, a 50Ah battery can theoretically deliver 5 amps for 10 hours before being fully discharged. However, this is a simplified measurement under ideal lab conditions.
The actual usable capacity is significantly less. A car battery is a starting battery, designed to deliver a very high current (measured in Cold Cranking Amps or CCA) for a few seconds to start the engine, not to be deeply discharged. Regularly draining it below 50% capacity can severely damage it. For applications requiring deep, sustained power, like in a RV or boat, you would use a deep-cycle battery with a similar Ah rating but built with thicker plates for durability.
Here is a table of typical amp-hour ratings for common car battery sizes (Group Sizes are standard industry classifications):
| Battery Group Size | Typical Vehicle Type | Common Amp-Hour (Ah) Range | Typical Cold Cranking Amps (CCA) |
|---|
| Group 35 | Midsize Sedans, Compact SUVs | 44 - 55 Ah | 500 - 650 CCA |
| Group 65 | Full-size Sedans, Trucks | 65 - 80 Ah | 650 - 850 CCA |
| Group 24 | Marine/RV (Dual-Purpose) | 70 - 85 Ah | 600 - 800 CCA |
| Group 34 | Large SUVs, Trucks | 50 - 60 Ah | 600 - 750 CCA |
| Group 48 (H6) | European Luxury Cars | 70 - 80 Ah | 700 - 900 CCA |
| Group 51R | Honda, Acura, Small Trucks | 45 - 60 Ah | 500 - 650 CCA |
To find your battery's exact Ah rating, check the manufacturer's label on the top or side of the battery. It's often listed as "20HR" or "C20" because the standard test involves discharging the battery over 20 hours.
