Your phone races from 10% to 70% in half an hour, then crawls through the last 20%. That isn't your charger failing. It's how lithium-ion batteries must be charged to stay safe and last longer.
The two phases of charging: CC and CV
Lithium-ion batteries are charged in two main stages:
1. Constant Current (CC)
The charger pushes a high, steady current while the battery voltage rises. This is the fast part, usually from low charge up to around 60–80%.
2. Constant Voltage (CV)
When the battery nears its maximum voltage (about 4.4–4.5V per cell on modern phones), the charger holds voltage steady and the current gradually tapers. This is the slow part, from about 80% to 100%.
Pushing high current near full voltage would overheat the battery and cause lithium plating and faster wear.
Why phones deliberately slow down
- Heat: the battery is already warm from fast charging.
- Battery health: high voltage plus high current accelerates ageing.
- Accuracy: the phone needs time to "top off" the cell precisely.
- Adaptive charging: phones may pause at 80% overnight on purpose.
Understanding marketing claims
Advertisements say things like "0–50% in 15 minutes" or "full charge in 30 minutes." Pay attention to:
- The starting point (often from 1–5%)
- Conditions (room temperature, phone idle, official charger)
- That 0–100% always takes much longer than twice the 0–50% time
Photo by Lukas Blazek on Pexels
Typical charging curve (example)
| Charge level | Relative speed |
|---|---|
| 0–50% | Fastest |
| 50–80% | Fast, starting to taper |
| 80–95% | Slow |
| 95–100% | Very slow trickle |
Tips to charge efficiently
- For quick top-ups, charge from 20% to 70–80%. It's the fastest and healthiest range.
- Keep the phone cool during charging.
- Use the official or certified charger that supports your phone's protocol.
- Enable charge limits (80%) if you don't need 100% daily.
Video explanation
Summary
Charging slows past 80% because lithium-ion batteries switch from constant current to constant voltage, tapering current to avoid heat and damage. It's a feature, not a fault, and charging to 80% is often all you need.
Compare phones with the fastest charging on infozme's fast charging phones list.
Cover photo by cottonbro studio on Pexels. This article was written with the help of AI.
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