Battery Temperature Derating
Ceff = Cnom × factor
Quick answer
This calculator solves Ceff = Cnom × factor for Effective Capacity. With Nominal Capacity 5.5 Ah, Derating Factor 50 %, the result is 2.75 Ah. It solves in 3 directions, so you can enter the values you have and get the one you need.
Calculator
Formula
Description
Battery capacity decreases at temperatures below the rated specification (typically 25°C) because the internal chemical reactions slow down and internal resistance increases. At 0°C, lithium-ion batteries deliver roughly 70-80% of their rated capacity, and at -20°C only 40-60%. At elevated temperatures, capacity may slightly increase but cycle life degrades rapidly. The derating factor is obtained from the manufacturer temperature-capacity curves and applied to the nominal capacity to determine the usable capacity at the operating temperature.
Variables
- Ceff — Effective usable capacity at operating temperature (mAh)
- Cnom — Nominal capacity at 25°C (mAh)
- factor — Temperature derating factor (0 to 1)
Practical Notes
Typical derating factors for Li-ion: 0°C = 0.75, -10°C = 0.60, -20°C = 0.45, -30°C = 0.30. Lead-acid batteries have even steeper derating. For outdoor or automotive applications, always size the battery for the minimum expected temperature. Battery heaters are used in EVs and satellite applications to maintain operating temperature.
Symbols and units
| Symbol | Meaning | Default unit | Accepted units |
|---|---|---|---|
| Ceff | Effective Capacity | mAh | mAh, Ah |
| Cnom | Nominal Capacity | mAh | mAh, Ah |
| factor | Derating Factor | — | —, % |
Step by step
- 1. What you know: Nominal Capacity 5.5 Ah, Derating Factor 50 %
- 2. The relation: Ceff = Cnom × factor
- 3. Substitute: Cnom = 5.5 Ah, factor = 50 %
- 4. Result: Effective Capacity = 2.75 Ah
Worked examples
Minimum range
Given: Nominal Capacity 110 mAh, Derating Factor 2.5 %
Result: Effective Capacity = 2.75 mAh
Low range
Given: Nominal Capacity 1.1 Ah, Derating Factor 25 %
Result: Effective Capacity = 0.275 Ah
Typical
Given: Nominal Capacity 5.5 Ah, Derating Factor 50 %
Result: Effective Capacity = 2.75 Ah
High range
Given: Nominal Capacity 22 Ah, Derating Factor 0.8
Result: Effective Capacity = 17.6 Ah
Maximum range
Given: Nominal Capacity 220 Ah, Derating Factor 8
Result: Effective Capacity = 1760 Ah
Solving for each variable
Solve for Effective Capacity
Nominal Capacity 110 mAh, Derating Factor 2.5 % → 2.75 mAh
Solve for Nominal Capacity
Effective Capacity 50 mAh, Derating Factor 2.5 % → 2 Ah
Solve for Derating Factor
Effective Capacity 50 mAh, Nominal Capacity 110 mAh → 45.45 %
How Effective Capacity changes with Nominal Capacity
| Nominal Capacity (input) | Effective Capacity (result) |
|---|---|
| 0.55 Ah | 0.275 Ah |
| 1.375 Ah | 0.6875 Ah |
| 2.75 Ah | 1.375 Ah |
| 4.125 Ah | 2.063 Ah |
| 5.5 Ah | 2.75 Ah |
| 8.25 Ah | 4.125 Ah |
| 11 Ah | 5.5 Ah |
| 22 Ah | 11 Ah |
| 38.5 Ah | 19.25 Ah |
| 55 Ah | 27.5 Ah |
The same result in other units
| Unit | Value |
|---|---|
| mAh | 2750 |
| Ah | 2.75 |
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<p><a href="https://vbatpower.com/formulas/battery-temp-derating/">Battery Temperature Derating</a> Calculator by vbatpower.com</p>Frequently asked questions
How do you calculate Battery Temperature Derating?
Use Ceff = Cnom × factor. With Nominal Capacity 5.5 Ah, Derating Factor 50 %, Effective Capacity works out to 2.75 Ah.
How do you calculate battery derating factor?
Rearrange for Effective Capacity: with Nominal Capacity 1.1 Ah, Derating Factor 25 %, Effective Capacity is 0.275 Ah.
What is the formula for Battery Temperature Derating?
The formula is Ceff = Cnom × factor. Battery capacity decreases at temperatures below the rated specification (typically 25°C) because the internal chemical reactions slow down and internal resistance increases.
How do you find Nominal Capacity when you know the other values?
Rearrange for Nominal Capacity: with Effective Capacity 50 mAh, Derating Factor 2.5 %, Nominal Capacity is 2 Ah.
How do you find Derating Factor when you know the other values?
Rearrange for Derating Factor: with Effective Capacity 50 mAh, Nominal Capacity 110 mAh, Derating Factor is 45.45 %.
What units does Battery Temperature Derating use?
Effective Capacity is shown in mAh, Ah. Values are held in SI base units internally, so you can mix prefixes without converting by hand.
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