Understanding Battery Reserve Capacity & Amp-Hour Ratings
RC and Ah ratings help you understand how long your battery can deliver power — especially in emergencies or low-charging conditions.
What Is Reserve Capacity (RC)?
- RC tells you how long (in minutes) a fully charged battery can run your vehicle if the alternator fails.
- Measured in minutes
- Simulates real world accessory usage without engine power
- Example: An RC of 90 means the battery can run for 90 minutes at 25 amps
Keep in mind: Battery capacity decreases over time — RC is measured when brand new.
Why it matters: A higher RC gives you more time to run electronics, lights, and power steering if your charging system fails.
What Is Amp-Hour (Ah)?
- Measures how much energy a battery can store and deliver over time
- Commonly used for deep cycle and leisure batteries
- Measured at the 20-hour rate (C20)
- Example: A 70Ah battery can deliver 3.5 amps for 20 hours
Why it matters: Ah ratings estimate runtime in steady-use situations — ideal for RVs, boats, or solar applications.
RC vs. Ah – What’s the Difference?
| Feature | Reserve Capacity (RC) | Amp-Hour (Ah) |
|---|---|---|
| Measures | Runtime in minutes | Capacity over time |
| Usage Focus | Starting + emergency backup | Deep cycle + steady usage |
| Typical Vehicles | Cars, trucks, SUVs | RVs, marine, golf carts |
Choosing the Right Rating
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Note: Most automotive and marine batteries don't list Ah rating. For reference, you can roughly estimate Ah from RC by multiplying RC × 0.6 (based on a 25-amp RC test). Golf cart batteries may also use RC measured at 75 amps.
Pro Tip: Match Battery to Usage
- Daily driver? Prioritize RC
- Off-grid or auxiliary power? Prioritize Ah
- Cold climates? Check Cold Cranking Amps (CCA) too
Need More Help?
Use our Battery Finder Tool to choose the right battery for your vehicle and lifestyle.
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