# Battery Charge Time Calculator

URL: https://speedycalculator.com/calculators/everyday-life/battery-charge-time/
Last updated: 2026-10-25

> The battery charge time calculator estimates how long it takes to charge a lithium-ion, lead-acid, NiMH or NiCd battery from its capacity, current state of charge and the charging current, allowing for charging efficiency.

## Inputs

- Battery capacity (Ah, mAh)
- Current charge level (%)
- Target charge level (%)
- Charging current (A, mA)
- Battery type (efficiency)

## Results

- Charge needed
- Charging time
- Charging time (h min)
- Charge rate (C-rate)

## Formula

```
Charge needed = capacity × (target − current state of charge)
Charge time = charge needed ÷ (charging current × efficiency)
```

## Explanation

Charging is never 100% efficient: lithium-ion batteries store about 95% of the charge put in, lead-acid about 85% and nickel batteries 70–80%. Real chargers also slow down near full (the constant-voltage phase), so charging the last 10–20% takes longer than the simple estimate.

### How to use the Battery Charge Time Calculator

- **Battery capacity**
- **Current charge level**
- **Target charge level**
- **Charging current**
- **Battery type (efficiency)**

Results update as you type, and every field accepts the units shown in its menu.

### How it works

Enter the battery capacity, the current and target state of charge, the charging current and the battery chemistry.

### Tips

- Use the figures printed on your product or its manual when you have them.
- Round quantities up so you are never short.
- Measure twice before you buy anything cut to size.
- Everything runs in your browser – try different values to compare options.

### Common mistakes to avoid

- Mixing units (inches and centimetres, mAh and Ah).
- Ignoring efficiency losses and safety margins.
- Treating rules of thumb as exact.

### Inputs explained

FieldWhat to enterBattery capacityUnits: Ah, mAhCurrent charge levelIn %Target charge levelIn %Charging currentUnits: A, mABattery type (efficiency)Choose one: Lithium-ion / LiPo (95%), LiFePO4 (96%), Lead-acid (85%), NiMH (80%) …

### What each result means

- **Charge needed** = [Battery capacity]×max([Target charge level] - [Current charge level], 0)÷100
- **Charging time** = [Charge needed]÷([Charging current]×[Battery type (efficiency)])
- **Charging time (h min)** = [Charging time]
- **Charge rate (C-rate)** = [Charging current]÷[Battery capacity]

### Example values

How the main result changes when **Battery capacity** changes and everything else stays at the example values above:

Battery capacity (Ah)Charging time (h)2.51.053.751.5852.116.252.637.53.16104.21

## Worked example

Inputs — Battery capacity: 5 Ah; Current charge level: 20 %; Target charge level: 100 %; Charging current: 2 A; Battery type (efficiency): Lithium-ion / LiPo (95%).

Results — Charge needed = 4 Ah; **Charging time = 2.11 h**; Charging time (h min) = 2 h 6 min; Charge rate (C-rate) = 0.4 C.

## FAQ

**How long does it take to charge a 5,000 mAh power bank at 2 A?**
From 20% to 100%, about 2 h 6 min, plus a little extra at the end.

**Why does the last 20% charge slowly?**
Lithium batteries switch to constant-voltage charging near full, so current tapers off.

**What is a safe charging current?**
Often 0.5–1C for lithium-ion; check the battery's datasheet.

**What formula does the Battery Charge Time Calculator use?**
Charge needed = capacity × (target − current state of charge).


## Sources

- [Battery University – Charging lithium-ion](https://batteryuniversity.com/)