Battery Charge Time
t = Capacity / Icharge
Quick answer
This calculator solves t = Capacity / Icharge for Charge Time. With Battery Capacity 2.5 Ah, Charge Current 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
Charge time estimates how long it takes to fully charge a battery at a given constant current. This is a simplified model because real charging profiles are not constant current throughout. Lithium-ion batteries use CC-CV (constant current then constant voltage) charging, where the current tapers during the CV phase, adding 30-60 minutes to reach full charge. The practical charge time is typically 1.2-1.5 times this theoretical value. Fast charging at higher currents reduces time but generates more heat and may reduce cycle life.
Variables
- t — Approximate charge time (h)
- Capacity — Battery capacity (mAh)
- Icharge — Charging current (mA)
Practical Notes
Standard lithium-ion charging is at 0.5C to 1C (where C is the capacity in Ah). A 3000mAh cell at 1C charges at 3A. Fast charging protocols (Qualcomm QC, USB-PD) use higher currents or voltages. NiMH batteries can be charged at up to 1C with proper termination. Lead-acid batteries charge best at C/10 to C/5 rate.
Symbols and units
| Symbol | Meaning | Default unit | Accepted units |
|---|---|---|---|
| t | Charge Time | h | ps, ns, µs, ms, s, min, h |
| Cap | Battery Capacity | mAh | mAh, Ah |
| Icharge | Charge Current | mA | mA |
Step by step
- 1. What you know: Battery Capacity 2.5 Ah, Charge Current 20 mA
- 2. The relation: t = Capacity / Icharge
- 3. Substitute: Cap = 2.5 Ah, Icharge = 20 mA
- 4. Result: Charge Time = 125 h
Worked examples
Minimum range
Given: Battery Capacity 50 mAh, Charge Current 0.1 mA
Result: Charge Time = 500 h
Low range
Given: Battery Capacity 0.5 Ah, Charge Current 1 mA
Result: Charge Time = 500 h
Typical
Given: Battery Capacity 2.5 Ah, Charge Current 20 mA
Result: Charge Time = 125 h
High range
Given: Battery Capacity 10 Ah, Charge Current 500 mA
Result: Charge Time = 20 h
Maximum range
Given: Battery Capacity 100 Ah, Charge Current 5000 mA
Result: Charge Time = 20 h
Solving for each variable
Solve for Charge Time
Battery Capacity 50 mAh, Charge Current 0.1 mA → 500 h
Solve for Battery Capacity
Charge Time 6 min, Charge Current 0.1 mA → 0.01 mAh
Solve for Charge Current
Charge Time 6 min, Battery Capacity 50 mAh → 500 mA
How Charge Time changes with Battery Capacity
| Battery Capacity (input) | Charge Time (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-charge-time/">Battery Charge Time</a> Calculator by vbatpower.com</p>Frequently asked questions
How do you calculate Battery Charge Time?
Use t = Capacity / Icharge. With Battery Capacity 2.5 Ah, Charge Current 20 mA, Charge Time works out to 125 h.
What is the formula for Battery Charge Time?
The formula is t = Capacity / Icharge. Charge time estimates how long it takes to fully charge a battery at a given constant current.
How do you find Battery Capacity when you know the other values?
Rearrange for Battery Capacity: with Charge Time 6 min, Charge Current 0.1 mA, Battery Capacity is 0.01 mAh.
How do you find Charge Current when you know the other values?
Rearrange for Charge Current: with Charge Time 6 min, Battery Capacity 50 mAh, Charge Current is 500 mA.
What units does Battery Charge Time use?
Charge Time 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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