Technical Insights
What Does 1C, 3C or 5C Mean on a Lithium Battery?
Convert C-rate into current and power, then check whether the rating is continuous, pulse, charge or discharge under stated conditions.
Quick answer
C-rate expresses current relative to rated capacity. For a 2.5 Ah cell, 1C equals 2.5 A, 3C equals 7.5 A and 5C equals 12.5 A. The label is incomplete unless it states charge or discharge, continuous or pulse duration, temperature, voltage cutoff and the capacity basis used.
Convert C-rate to amperes
Use:
Current (A) = C-rate × rated capacity (Ah)
| Rated capacity | 1C | 3C | 5C |
|---|---|---|---|
| 1.0 Ah | 1 A | 3 A | 5 A |
| 2.5 Ah | 2.5 A | 7.5 A | 12.5 A |
| 5.0 Ah | 5 A | 15 A | 25 A |
For an approximate cell-level power check, multiply current by operating voltage. Because battery voltage changes during discharge, power also changes.
Continuous and pulse ratings are different
A continuous rating applies under specified thermal and cutoff conditions without exceeding allowed limits. A pulse rating applies only for a stated duration, rest interval and starting state of charge. “5C” without these conditions cannot support pack design or supplier comparison.
The pack’s current limit may be lower than the cell-level calculation because of:
- BMS current and thermal limits;
- nickel or copper interconnect resistance;
- connector, cable and fuse ratings;
- cell-to-cell temperature differences;
- enclosure cooling;
- required service-life margin.
C-rate affects capacity, heat and lifetime
Higher current increases resistive heating approximately with the square of current for a given resistance. Voltage sag can reach the equipment cutoff earlier, reducing delivered energy. Repeated high-rate operation at elevated temperature can shorten life even when it stays inside an absolute maximum rating.
Capacity is also measured at a specified discharge rate. A cell advertised at 5 Ah may deliver a different usable capacity at 5C than in the lower-rate capacity test.
Questions buyers should ask
- Is the rating for charge or discharge?
- Is it continuous or pulse, and what is the pulse duration and rest time?
- What are the temperature and voltage cutoff conditions?
- What capacity test rate establishes the Ah value?
- What maximum temperature is permitted at the cell and pack level?
- Does the BMS, connector and interconnect support the same current?
Select a cell with margin above the real duty cycle. Do not design a pack to operate continuously at an unexplained headline maximum.
FAQ
Does a 5C battery fully discharge in 12 minutes?
The mathematical rate corresponds to 1/5 hour, but usable capacity, voltage cutoff and temperature at high current may prevent the rated capacity from being delivered in practice.
Is charge C-rate the same as discharge C-rate?
No. A cell may permit high discharge current but a much lower charge current. Check both limits separately.