Battery Life of 4000 mAh at 300 mA Smartphone
A 4000 mAh smartphone battery under a 300 mA average load at 75% efficiency lasts approximately 10 hours.
How to use this tool
- Enter battery capacity, average load current and derating efficiency in the fields above.
- Results update instantly as you type — or click Calculate.
- Read your battery life and the full breakdown beneath it.
Estimate real-world smartphone screen-on time for a 4000 mAh battery discharging at a moderate 300 mA average current.
Frequently asked questions
- Why use a derating efficiency?
- Manufacturers rate capacity at a slow discharge rate (C/20). At higher currents or in cold temperatures, actual capacity is lower. 70% is a conservative real-world rule for lithium-ion cells.
- How do I find my device's current draw?
- Check the datasheet. For variable loads take a weighted average: active current × active fraction + sleep current × sleep fraction.