Introduction
Walk into any auto parts store looking for a battery and you'll be confronted with a bewildering array of numbers and specifications. CCA, Ah, RC, group sizes—what does it all mean, and how do you know which specifications matter for your vehicle?
This guide decodes battery specifications, explaining what each measurement represents and why it matters. Armed with this knowledge, you'll be able to make informed decisions about battery selection and understand why some batteries cost more than others.
Cold Cranking Amps (CCA)
CCA is arguably the most important specification for Australian drivers, despite our generally mild climate.
The Definition
Cold Cranking Amps measures the current (in amperes) a battery can deliver for 30 seconds at -18°C while maintaining at least 7.2 volts.
Why It Matters
Starting an engine requires an enormous amount of current—often 200-400 amps for a few seconds. The CCA rating tells you how well a battery can deliver this power, especially in challenging conditions.
Higher CCA means:
What About Australia?
While we don't experience -18°C temperatures except in alpine regions, CCA remains relevant because:
How Much CCA Do You Need?
As a minimum, match your vehicle manufacturer's specification. Beyond that:
Reserve Capacity (RC)
Reserve Capacity is often overlooked but can be crucial in emergencies.
The Definition
RC measures how many minutes a fully charged battery can deliver 25 amps at 27°C before the voltage drops below 10.5 volts (the minimum needed to keep most vehicles running).
Why It Matters
This specification tells you how long you can run on battery power alone if your alternator fails. A higher RC gives you more time to:
Real-World Applications
Higher Reserve Capacity is particularly valuable for:
Typical Values
Most passenger car batteries have an RC between 60 and 120 minutes. Larger batteries typically have higher reserve capacity.
Amp Hours (Ah)
This specification measures total energy storage capacity.
The Definition
Amp Hours indicates how much current a battery can supply over a specified period. A 60Ah battery can theoretically deliver:
In practice, the relationship isn't perfectly linear—batteries deliver more total energy at lower discharge rates.
Why It Matters
Higher Ah means more stored energy. This is important for:
Relationship to Other Specifications
Batteries with higher Ah generally also have higher CCA and RC. However, the relationship isn't fixed—a battery optimised for high CCA might have lower Ah than one optimised for deep cycle use.
Cranking Amps (CA) vs. CCA
These specifications are related but not interchangeable.
The Difference
Because batteries perform better in warmer conditions, the CA number is always higher than CCA for the same battery—typically 20-25% higher.
Marketing Concerns
Some budget batteries advertise high CA numbers while having modest CCA ratings. Always compare CCA to CCA for accurate comparison.
Which to Use?
CCA is the industry standard for comparison. Use CCA when evaluating batteries; if only CA is provided, assume the CCA is about 80% of that figure.
Marine Cranking Amps (MCA)
Another related specification, primarily used for marine batteries.
The Definition
MCA is measured at 0°C (same as CA) but is specifically designed for marine applications where extreme cold is less common than in automotive use.
For Car Buyers
Unless you're buying a battery for a boat, MCA isn't relevant. If you see this specification on an automotive battery, look for the CCA rating instead.
Battery Group Size
This specification determines physical compatibility.
What It Means
Battery group sizes are standardised dimensions that ensure batteries fit properly in different vehicles. A group size defines:
Common Australian Group Sizes
Some common group sizes in Australia include:
Getting It Right
The correct group size ensures your battery:
Using the wrong size can mean cables that don't reach, batteries that move around, or bonnets that don't close properly.
Voltage
All standard car batteries are 12-volt nominal, but understanding voltage behaviour is still useful.
At Rest
A fully charged, healthy 12V battery should read approximately 12.6-12.8 volts when at rest (not being charged or discharged).
While Charging
During charging (alternator running), voltage should be 13.5-14.5 volts. Higher suggests overcharging; lower indicates undercharging.
Voltage vs. State of Charge
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Battery Chemistry and Type
Different battery technologies have different characteristics.
Standard Flooded (Wet Cell)
The traditional design with liquid electrolyte.
AGM (Absorbent Glass Mat)
Premium technology with electrolyte absorbed in fibreglass.
EFB (Enhanced Flooded Battery)
A middle ground designed for start-stop systems.
Which Type for Your Vehicle?
Putting It All Together
When selecting a battery, prioritise specifications in this order:
Conclusion
Battery specifications might seem confusing at first, but they serve important purposes. CCA tells you about starting power, RC and Ah indicate energy storage, and group size ensures proper fit.
When shopping for batteries, focus on finding one that meets your vehicle's requirements (check your owner's manual), then consider whether extra capacity or premium technology is worthwhile for your situation.