4000mAh battery with 18W charger at 20% current level:
Result: ~1 hour 45 minutes
This provides an estimate based on standard charging physics. Actual time may vary due to temperature, battery health, and other factors.
Many devices slow down charging when reaching 80% to protect battery health. Also check for poor-quality cables.
Frequent use of very fast charging (50W+) may slightly reduce long-term battery capacity.
This accounts for energy lost as heat during charging. Most chargers are 70-90% efficient.