Calculator
Example Data Table
| Capacity | SOC | Tariff | Grid Energy (kWh) | Cost / Session | Time (h) |
|---|---|---|---|---|---|
| 60 ah @ 12V | 20% → 100% | Flat $0.20/kWh | 0.714774 | $0.1430 | 2.3435 |
Formula Used
1) Convert capacity to energy:
- kWh = kWh
- kWh = Wh / 1000
- kWh = (Ah × V) / 1000
- kWh = (mAh ÷ 1000 × V) / 1000
2) Energy added to the battery:
E_batt(kWh) = Capacity_kWh × (SOC_target − SOC_start) / 100
3) Combined efficiency:
η = (η_charger/100) × (η_battery/100) × (1 − losses/100)
4) Grid energy and standby:
E_grid_base = E_batt / η
E_standby = (P_standby × time_h) / 1000
E_grid_total = E_grid_base + E_standby
5) Time estimate:
time_h ≈ (E_grid_base × 1000) / P_input(W)
6) Cost:
Cost_session = (E_grid_total × rate_effective) + fee_fixed
How to Use This Calculator
- Choose a tariff: flat rate or time-of-use.
- Enter your battery capacity and select the unit.
- If using Ah or mAh, provide nominal voltage.
- Set start and target state of charge values.
- Fill efficiency and loss fields using your best estimates.
- Select how to estimate time: power, current, or hours.
- Add standby power and any fixed fee if needed.
- Press Calculate to see results above the form.
- Use the download buttons to export CSV or PDF.
FAQs
1) Why is grid energy higher than battery energy?
Some energy is lost as heat in the charger, cables, and battery chemistry. Lower efficiency and higher standby power increase the difference.
2) Which capacity unit should I use?
Use kWh or Wh if you already know energy. Use Ah or mAh when your battery label shows charge capacity, and add nominal voltage for conversion.
3) How accurate is the charging time estimate?
It is an approximation. Many chargers taper current near full charge, so real time can be longer than the constant-power estimate.
4) What efficiency numbers are reasonable?
Common AC chargers range around 85–95% efficient. Battery acceptance varies by chemistry and temperature, often around 90–98% for typical systems.
5) How does time-of-use pricing work here?
The calculator splits total grid energy by your peak share percentage, then applies peak and off-peak rates. It does not model a full hourly schedule.
6) What should I enter for standby power?
Use the average extra draw during charging: fans, displays, controllers, and battery management. If unknown, start with 0–10 W and refine later.
7) Can this estimate monthly and yearly charging costs?
Yes. Enter sessions per month to scale per-session cost into monthly and yearly totals. It is helpful for budget planning and comparisons.
8) Why add a fixed fee per session?
Some charging locations add per-connection or service fees. This field lets you include those fees alongside energy costs for a more realistic total.