Battery charging time calculator

The general formula is:

Or in a more readable way:

Where:

• T = Charging time (in hours)
• C = Battery capacity (in mAh or Ah)
• I = Charging current (in mA or A)
• η = Charging efficiency (usually 0.8 to 0.9 for lithium-ion)

Notes & Real-World Factors

• 🔋 Charging current (I) depends on your charger rating and what the battery can accept.
• ⚡ Efficiency (η) is rarely 100% — heat loss and internal resistance reduce it.
• 📉 The last 10–20% of charging is usually slower due to constant voltage mode (especially in Li-ion).
• 🪫 If battery is deeply discharged, charging might be even slower initially.