Charge time is capacity divided by current—plus real-world loss from heat and taper. This guide walks through the battery charging time calculator: mAh, charger mA, and efficiency % for a realistic refill estimate.
Benefits
- Base formula: hours = mAh ÷ mA, then ÷ (efficiency ÷ 100).
- Efficiency field models taper and heat loss (try 85–95%).
- Pairs with Battery Runtime for discharge-then-recharge planning.
How it works
- Enter battery capacity in mAh from the label or datasheet.
- Add charger output current in mA (wall brick, USB-C PD, or bench supply).
- Set charge efficiency %—read estimated time to full.
FAQ
How does the battery charging time calculator work?
Time (h) = mAh ÷ mA ÷ (efficiency ÷ 100). Example: 5,000 mAh at 2,000 mA and 90% efficiency → 5,000 ÷ 2,000 ÷ 0.9 ≈ 2.78 hours. At 100% efficiency the base time is 2.5 hours; loss adds margin.
What efficiency should I use?
Use 100% for a theoretical upper bound. For Li-ion with CC/CV taper, 85–95% is typical—lower for fast chargers or cold packs. The tool note on the calculator reminds you that taper above ~80% SoC extends real-world time.
Can I use this for 12 V Ah banks?
Convert Ah to mAh first (× 1,000), then use charger amps as mA (× 1,000). Example: 100 Ah at 20 A charge → 100,000 mAh ÷ 20,000 mA = 5 h base before efficiency. Voltage cancels in the mAh/mA ratio when both are at the same bus.
Technical specifications
- Charge time (h) = capacity_mAh ÷ current_mA ÷ (efficiency% ÷ 100).
- C-rate hint: current_mA ÷ capacity_mAh ≈ C (1C → ~1 h at 100% eff.).
- Taper: expect longer than calc above ~80% SoC unless eff is lowered.
- Related: battery-charging-time, battery-runtime, solar-panel-size.