Battery Runtime
t = Capacity / Current
Quick answer
This calculator solves t = Capacity / Current for Runtime. With Battery Capacity 2.5 Ah, Load Current (mA) 20 mA, the result is 125 h. It solves in 3 directions, so you can enter the values you have and get the one you need.
Calculator
Formula
Description
Battery runtime is estimated by dividing the battery capacity by the average load current, giving the theoretical number of hours until the battery is depleted. A 3000mAh battery supplying 500mA gives a theoretical runtime of 6 hours. However, real-world runtime is typically 70-85% of this theoretical value due to several factors: the Peukert effect (higher discharge rates reduce effective capacity), voltage regulator efficiency losses, and the minimum voltage cutoff of the circuit which leaves some energy unused in the battery.
Variables
- t — Runtime in hours (h)
- Capacity — Battery capacity in milliamp-hours (mAh)
- Current — Average load current in milliamps (mA)
Practical Notes
Battery capacity is rated at a specific discharge rate (typically C/20 for lead-acid, C/5 for lithium). Drawing current faster than the rated discharge rate reduces the usable capacity. For pulsed loads, use the average current including sleep modes. Temperature also significantly affects capacity: lithium batteries lose 20-30% capacity at 0°C compared to 25°C.
Symbols and units
| Symbol | Meaning | Default unit | Accepted units |
|---|---|---|---|
| t | Runtime | h | ps, ns, µs, ms, s, min, h |
| Cap | Battery Capacity | mAh | mAh, Ah |
| I | Load Current (mA) | mA | mA |
Step by step
- 1. What you know: Battery Capacity 2.5 Ah, Load Current (mA) 20 mA
- 2. The relation: t = Capacity / Current
- 3. Substitute: Cap = 2.5 Ah, I = 20 mA
- 4. Result: Runtime = 125 h
Worked examples
Minimum range
Given: Battery Capacity 50 mAh, Load Current (mA) 0.1 mA
Result: Runtime = 500 h
Low range
Given: Battery Capacity 0.5 Ah, Load Current (mA) 1 mA
Result: Runtime = 500 h
Typical
Given: Battery Capacity 2.5 Ah, Load Current (mA) 20 mA
Result: Runtime = 125 h
High range
Given: Battery Capacity 10 Ah, Load Current (mA) 500 mA
Result: Runtime = 20 h
Maximum range
Given: Battery Capacity 100 Ah, Load Current (mA) 5000 mA
Result: Runtime = 20 h
Solving for each variable
Solve for Runtime
Battery Capacity 50 mAh, Load Current (mA) 0.1 mA → 500 h
Solve for Battery Capacity
Runtime 6 min, Load Current (mA) 0.1 mA → 0.01 mAh
Solve for Load Current (mA)
Runtime 6 min, Battery Capacity 50 mAh → 500 mA
How Runtime changes with Battery Capacity
| Battery Capacity (input) | Runtime (result) |
|---|---|
| 0.25 Ah | 12.5 h |
| 0.625 Ah | 31.25 h |
| 1.25 Ah | 62.5 h |
| 1.875 Ah | 93.75 h |
| 2.5 Ah | 125 h |
| 3.75 Ah | 187.5 h |
| 5 Ah | 250 h |
| 10 Ah | 500 h |
| 17.5 Ah | 875 h |
| 25 Ah | 1250 h |
The same result in other units
| Unit | Value |
|---|---|
| s | 450000 |
| min | 7500 |
| h | 125 |
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<p><a href="https://vbatpower.com/formulas/battery-runtime/">Battery Runtime</a> Calculator by vbatpower.com</p>Frequently asked questions
How do you calculate Battery Runtime?
Use t = Capacity / Current. With Battery Capacity 2.5 Ah, Load Current (mA) 20 mA, Runtime works out to 125 h.
What is the formula for Battery Runtime?
The formula is t = Capacity / Current. Battery runtime is estimated by dividing the battery capacity by the average load current, giving the theoretical number of hours until the battery is depleted.
How do you find Battery Capacity when you know the other values?
Rearrange for Battery Capacity: with Runtime 6 min, Load Current (mA) 0.1 mA, Battery Capacity is 0.01 mAh.
How do you find Load Current (mA) when you know the other values?
Rearrange for Load Current (mA): with Runtime 6 min, Battery Capacity 50 mAh, Load Current (mA) is 500 mA.
What units does Battery Runtime use?
Runtime is shown in s, min, h. Values are held in SI base units internally, so you can mix prefixes without converting by hand.
Related Concepts
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