C20 Capacity (Ampere-Hour)
What Is C20?
C20 measures a battery's energy storage capacity in ampere-hours (Ah) when discharged at a constant current over 20 hours at 25degC, until voltage reaches 10.5V. Example: a 65Ah (C20) battery delivers 3.25A for 20 hours.
C20 is the industry standard capacity rating — it represents steady, long-duration discharge rather than the short-burst power that CCA measures.
Test Method (IEC 60095-1)
- Battery is fully charged and stabilized at 25degC +/- 2degC
- Discharge at C20 current = Rated Ah / 20 (e.g., 65Ah battery = 3.25A)
- Voltage is monitored throughout the 20-hour period
- Test ends when voltage reaches 10.5V or 20 hours elapse
- Pass: Actual capacity >= 95% of rated capacity
- Result is calculated as: C20 = Discharge current (A) x Discharge time (hours)
Why C20 Matters
- Energy storage: How long can the battery run accessories with the engine off?
- System sizing: Does the battery capacity match the vehicle's electrical demand?
- Deep cycle suitability: Higher C20 = better tolerance for repeated discharge
- Market specification: Many markets specify battery requirements in Ah, not CCA
Capacity vs. Discharge Rate
| Discharge Rate | Typical Capacity (% of C20) | Usage |
|---|---|---|
| C20 (20-hour) | 100% | Industry standard rating |
| C10 (10-hour) | ~93% | UPS/telecom rating |
| C5 (5-hour) | ~85% | Faster discharge — used for traction batteries |
| C1 (1-hour) | ~65% | High-rate discharge |
Batteries deliver less total energy at higher discharge rates due to internal resistance and electrolyte diffusion limitations (Peukert's Law).
Chengguang Model Capacity Reference
| Model | C20 (Ah) | Vehicle Class |
|---|---|---|
| 55B24 | 45 | Compact cars |
| 65D26 | 55-70 | Mid-large sedans, SUVs |
| 105D31 | 90 | Large SUVs, pickups |
| 95E41 | 100 | Large SUVs, diesel |
| 145G51 | 120-135 | Medium trucks |
| 190H52 | 200 | Heavy trucks, equipment |
| 60038 | 100 | European luxury/large |
Author: Chengguang Power Tech Engineering Team | Reference: IEC 60095-1