Charging a phone battery
Pick a phone battery of 3000, 4000 or 5000 mAh and a 1 A, 2 A or 3 A charger. Work out how long it takes to charge from empty, how much energy it stores and how many hours the screen can stay on.
Core concept
A battery's capacity in mAh is the charge it holds: hours to charge = capacity ÷ charger current (plus about 20% losses), and energy in Wh = capacity (Ah) × voltage
Topic: Energy and technology
A phone battery's capacity is printed in milliampere-hours (mAh). A 5000 mAh battery holds enough charge to give 5000 mA (5 A) for one hour, or 400 mA for 12.5 hours. Charge = current: The flow of electricity through a wire, measured in amperes (A). All key words × time, so the time to fill it is the capacity divided by the charger's current: a 2 A (2000 mA) charger needs 2.5 hours, and about 20% more because some energy: What is needed to make things move, heat up, light up or grow. All key words is lost as heat and charging slows near full. The energy stored is the charge times the battery's voltage: The push that makes electricity flow, measured in volts (V). All key words, about 3.85 V: 5 Ah × 3.85 V = 19.25 watt-hours (Wh). A phone with its screen on uses roughly 400 mA, which tells us how long the battery lasts.
What you will learn
- Explain what mAh means as an amount of charge.
- Work out charging time from capacity and charger current.
- Find the energy stored in Wh from capacity and voltage.
Before you start
- Know that charge = current × time.
Materials
- Your family's phone and charger (read the labels; do not open them)
Equipment
- None
Procedure
- Record the 5000 mAh battery on a 2 A charger.
- Change to a 1 A charger, then a 3 A charger, and record each.
- Change to a 3000 mAh battery and record.
How this simulation is simplified
- The battery works at 3.85 V; charging loses about 20% (so the time is × 1.2).
- A phone with its screen on uses about 400 mA.