Battery C-Rate Reference
Quick-reference table for converting between C-rate and actual current. Know exactly how many amps your battery can charge or discharge at each rate.
C-Rate Explained
C-rate is the standard way to express charge or discharge current relative to a battery's capacity. It normalizes current across different battery sizes. A 1C rate on a 100Ah battery is 100A; on a 50Ah battery, 1C is 50A. Both batteries are being charged or discharged at the same relative stress level.
Common C-rates range from 0.05C (trickle charging) to 3C (high-power discharge). The "C" in C-rate stands for capacity. The number before C indicates the multiplier. 0.5C means half the capacity in amps. 2C means twice the capacity in amps.
Time to charge or discharge is inversely proportional to C-rate. At 0.2C, it takes 5 hours. At 0.5C, it takes 2 hours. At 1C, it takes 1 hour. At 2C, it takes 30 minutes. This relationship holds regardless of battery size.
C-rate current equals battery capacity multiplied by C-rate.
C-rate current equals battery capacity multiplied by C-rate.
Current Reference Table
The table below shows the actual current in amps for common battery capacities at each C-rate. Use this to quickly determine what current your battery should charge or discharge at.
| C-Rate | 50 Ah | 100 Ah | 200 Ah | 300 Ah | Approx. Time |
|---|---|---|---|---|---|
| 0.1C | 5 A | 10 A | 20 A | 30 A | ~10 hours |
| 0.2C | 10 A | 20 A | 40 A | 60 A | ~5 hours |
| 0.5C | 25 A | 50 A | 100 A | 150 A | ~2 hours |
| 1C | 50 A | 100 A | 200 A | 300 A | ~1 hour |
| 2C | 100 A | 200 A | 400 A | 600 A | ~30 minutes |
Approximate times assume constant current (CC phase only). Actual charge time includes CV phase and is longer.
Charging vs Discharging C-Rates
Batteries often have different maximum C-rates for charging and discharging. A battery that can discharge at 2C may only safely charge at 0.5C. This asymmetry exists because charging causes different chemical stresses than discharging — particularly lithium plating risk during high-rate charging.
Typical Charge C-Rates
LiFePO4: 0.5–1C (fast), 0.2C (gentle)
NMC: 0.5–1C (fast), 0.3C (gentle)
Lead-acid: 0.1–0.3C (limited by chemistry)
AGM: 0.2–0.4C (better than flooded)
Typical Discharge C-Rates
LiFePO4: 1–3C (continuous), 5–10C (peak)
NMC: 1–2C (continuous), 3–5C (peak)
Lead-acid: 0.1–0.3C (Peukert effect above this)
AGM: 0.2–0.5C (better high-rate than flooded)
Always check the manufacturer's datasheet for the specific C-rate limits of your battery. Exceeding the recommended C-rate voids warranties, reduces cycle life, and can create safety hazards.
Chemistry Considerations
Different battery chemistries respond differently to high C-rates. LiFePO4 handles high C-rates well with minimal degradation. Lead-acid suffers the Peukert effect — effective capacity drops significantly at high discharge rates. NMC falls between the two.
| Chemistry | Recommended Charge | Recommended Discharge | High C-Rate Tolerance |
|---|---|---|---|
| LiFePO4 | 0.2–0.5C | 0.5–1C | Excellent |
| NMC | 0.3–0.5C | 0.5–1C | Good |
| Lead-Acid | 0.1–0.3C | 0.1–0.2C | Poor (Peukert effect) |
| AGM | 0.2–0.4C | 0.2–0.3C | Moderate |
Common Mistakes
Confusing C-Rate with Absolute Current
1C means different currents for different batteries. 1C on a 50Ah battery is 50A; on a 200Ah battery, it is 200A. Always calculate the actual current from the C-rate and capacity before sizing wires, fuses, or BMS components.
Exceeding Manufacturer Limits
Just because a battery can physically deliver 2C does not mean it should. Exceeding the recommended C-rate accelerates degradation, voids warranties, and may create safety risks. Stay within the datasheet limits.
Ignoring Peukert Effect in Lead-Acid
Lead-acid batteries deliver less total energy at high discharge rates. A 100Ah lead-acid battery at 1C may only deliver 60–70Ah. LiFePO4 does not suffer this effect — it delivers close to rated capacity regardless of C-rate within limits.
Using Same C-Rate for Charge and Discharge
Charge and discharge C-rate limits are different. A battery rated for 1C discharge may only support 0.5C charge. Using the discharge rating for charging leads to overcharging stress and potential damage.
Try It
Use the C-Rate Calculator to convert between current, capacity, and C-rate for your specific battery configuration.
Open C-Rate CalculatorFrequently Asked Questions
What does 0.2C mean for a 100Ah battery?
0.2C means the charge or discharge current is 20% of the battery capacity. For a 100Ah battery, 0.2C = 20A. At this rate, the battery will theoretically charge or discharge in 5 hours (1 / 0.2 = 5). This is considered a slow, gentle rate that maximizes battery lifespan.
What is the difference between charge C-rate and discharge C-rate?
Charge C-rate is the current used to charge the battery, while discharge C-rate is the current drawn during use. Many batteries can handle higher discharge C-rates than charge C-rates. For example, a LiFePO4 battery might support 1C discharge but only 0.5C charge. Always check the manufacturer's specifications for both.
Which C-rate is best for battery longevity?
Lower C-rates produce less heat and stress, extending cycle life. For LiFePO4, 0.2–0.5C is ideal for daily cycling. For lead-acid, keeping discharge below 0.2C (5-hour rate) minimizes sulfation. Higher C-rates (1C+) are acceptable for occasional fast charging or high-power discharge but reduce overall lifespan.
How do I calculate the current from C-rate?
Multiply the C-rate by the battery capacity in Ah. Formula: Current (A) = C-Rate × Capacity (Ah). For example, 0.5C on a 200Ah battery = 0.5 × 200 = 100A. Reverse the formula to find C-rate from current: C-Rate = Current (A) / Capacity (Ah).