Enter Battery Data
Formula Used
1. Effective capacity
Effective Capacity (Ah) = Nominal Capacity × Available Capacity Factor
2. Effective stored energy
Effective Energy (Wh) = Effective Capacity × Nominal Voltage
3. SOC-based discharge
DoD (%) = Starting SOC − Ending SOC
4. SOC-based amp-hour use
Used Ah = Effective Capacity × DoD ÷ 100
5. Load-based battery draw
Battery Ah Drawn = (Current × Time) ÷ Efficiency
6. Load-based depth of discharge
DoD (%) = Battery Ah Drawn ÷ Effective Capacity × 100
7. Remaining runtime above reserve
Runtime = Usable Reserve Energy ÷ Load Power
8. Cycle stress index
Stress Index = Calculated DoD ÷ Recommended Daily Max DoD
This calculator treats discharge efficiency as a loss factor between battery energy and delivered load energy. SOC-based results take priority when both beginning and ending SOC values are provided.
How to Use This Calculator
- Select the battery chemistry that most closely matches your pack.
- Enter nominal capacity and nominal system voltage.
- Type the starting state of charge for the discharge event.
- Enter the ending state of charge if measured from monitoring equipment.
- Add discharge current and time to generate a load-based estimate.
- Set discharge efficiency to reflect inverter, wiring, and pack losses.
- Use the available capacity factor to model age or temperature derating.
- Set a reserve SOC limit to protect backup time and battery health.
- Submit the form and review the depth of discharge, reserve energy, runtime, and cycle stress indicators.
Example Data Table
| Battery Chemistry | Capacity (Ah) | Voltage (V) | Start SOC (%) | End SOC (%) | Current (A) | Time (h) | Efficiency (%) | Capacity Factor (%) | Calculated DoD (%) | Remaining Runtime Above Reserve (h) |
|---|---|---|---|---|---|---|---|---|---|---|
| Lithium Iron Phosphate (LiFePO4) | 100 | 12 | 100 | 55 | 9 | 5 | 92 | 95 | 45.00 | 3.40 |
| AGM Lead Acid | 200 | 24 | 95 | 60 | 15 | 4 | 88 | 90 | 35.00 | 2.82 |
| Flooded Lead Acid | 150 | 48 | 90 | 40 | 12 | 6 | 85 | 85 | 50.00 | 1.70 |
FAQs
1. What does depth of discharge mean?
Depth of discharge is the percentage of battery capacity removed during a discharge event. A 40% DoD means 40% of available stored energy has been used, while 60% remains in the battery.
2. Why does chemistry matter?
Different chemistries tolerate deep cycling differently. Lead-acid batteries usually prefer shallower daily discharge, while many lithium batteries can handle deeper cycling with less cycle life penalty when operated within rated conditions.
3. Why are SOC-based and load-based values sometimes different?
They can differ because monitoring data, voltage sag, efficiency assumptions, meter accuracy, temperature, and battery aging all affect the result. Comparing both methods helps identify inconsistent field measurements or unrealistic assumptions.
4. What is the available capacity factor?
It is a derating input for real-world conditions. Use it to reflect aging, cold temperatures, reduced maintenance condition, or other factors that lower the battery’s practical usable capacity.
5. Why keep a reserve state of charge?
A reserve improves system resilience and helps avoid excessively deep discharge. It is especially useful for backup systems, off-grid installations, and applications where voltage collapse or emergency autonomy matters.
6. Does this calculator estimate remaining runtime?
Yes. It estimates runtime above the selected reserve using current load power and usable remaining energy. It is most accurate when the load is relatively steady during the remaining discharge period.
7. Can I use this for solar and inverter systems?
Yes. The calculator works well for solar storage, UPS banks, telecom backup, marine systems, electric mobility support packs, and general engineering analysis where capacity and discharge conditions are known.
8. Is the cycle stress index a warranty figure?
No. It is a planning indicator based on recommended daily discharge depth. Always confirm final operating limits, cycle life expectations, and warranty conditions from the battery manufacturer’s documentation.