What is Milliamps Per Hour Calculation and Why Should You Care?
Understanding the relationship between battery capacity (mAh) and current draw (mA) is essential for anyone working with battery-powered devices. This calculation helps you determine how much current your device can draw while achieving your desired runtime.
Whether you're designing electronics, choosing batteries for a project, or estimating device runtime, this calculation is fundamental to proper battery sizing.
How to Calculate Current Draw from mAh
The formula for calculating current draw is:
[\text{Current (mA)} = \frac{\text{Battery Capacity (mAh)}}{\text{Runtime (hours)}}]
Where:
- Current is the maximum average current draw in milliamps
- Battery Capacity is the mAh rating of your battery
- Runtime is the desired operating time in hours
Calculation Example
If you have a 2000mAh battery and need 8 hours of runtime:
[\text{Current} = \frac{2000 \text{ mAh}}{8 \text{ hours}} = 250 \text{ mA}]
Your device should draw no more than 250mA on average to achieve 8 hours of operation.
Common Battery Capacities
| Battery Type | Typical Capacity |
|---|---|
| AAA | 1000-1200 mAh |
| AA | 2000-3000 mAh |
| 18650 Li-ion | 2500-3500 mAh |
| Phone Battery | 3000-5000 mAh |
| Laptop Battery | 40000-100000 mAh |
Practical Tips
- Plan for about 80% of theoretical capacity for real-world use
- Consider peak current draw, not just average
- Temperature affects battery performance significantly
- Battery capacity decreases with age and use cycles