Complete Guide to Battery Capacity
The Battery Capacity Calculator computes Ah needed for runtime at safe DoD. Prevents deep discharge.
What is Battery Capacity?
Ah = (W × hrs) / (V × DoD/100 × Eff/100). Our Battery Capacity Calculator includes inverter loss.
Why Limit DoD?
- Lead-Acid: 50% → 500 cycles.
- Li-ion: 80% → 2000+ cycles.
- AGM/Gel: 50–60%.
Use with Solar Output and Inverter Sizing.
DoD by Type
| Type | Max DoD | Cycles @ DoD |
|---|---|---|
| Lead-Acid | 50% | ~500 |
| AGM | 50–60% | ~800 |
| Gel | 50% | ~700 |
| Li-ion | 80–90% | 2000–5000 |
| NiMH | 70% | ~1000 |
Calculation Steps
- Wh: Power × Runtime.
- Ah: Wh / (V × DoD × Eff).
- Round Up: Next standard size.
Example: 12V Off-Grid
240W load, 5 hrs, Lead-Acid 50% DoD, 90% inverter.
- Wh = 240 × 5 = 1200
- Ah = 1200 / (12 × 0.5 × 0.9) = 222.2 Ah
- Use 2× 120Ah = 240Ah bank
Peukert’s Law
High discharge reduces effective Ah. Use 1.1–1.3 exponent for lead-acid.
Series/Parallel
- Series: V adds, Ah same.
- Parallel: Ah adds, V same.
Practical Tips
- Temperature: Derate 1%/°C below 25°C.
- Equalization: Lead-acid monthly.
- BMS: Required for Li-ion.
- Fuse: 1.25× max current.
Common Mistakes
- 100% DoD: Kills battery.
- Ignore Inverter Loss: Undersized.
- Mix Old/New: Imbalance.
- No Ventilation: Gas buildup.
Advanced
- C-Rate: Discharge rate.
- Self-Discharge: 3–5%/month (LA).
- Charge Controller: MPPT vs PWM.
- Autonomy Days: 2–3 for solar.
Conclusion
Proper sizing extends battery life. Our Battery Capacity Calculator ensures safe DoD. Pair with Solar and Construction tools. Power reliably with 1000 Calculators.