System Mode
Required Battery Capacity
—kWh
Total rated capacity to install
Inverter Size
—
recommended
📜 NEC Code Requirements (Article 706 — ESS)
✓ ESS >1 kWh requires NEC Article 706 compliance
✓ Emergency disconnect required — accessible from outside
✓ All DC conductors sized at 125% of max continuous current
✓ DC overcurrent devices must be UL-listed for DC
✓ Labeling required: chemistry, voltage, capacity, current
✓ Commissioning required before energization
⚠ FLA batteries require H₂ ventilation per NEC 706.30
Always verify with your local AHJ (Authority Having Jurisdiction) as requirements may exceed NEC minimums.
Capacity Degradation Over Time
Battery Chemistry Reference
| Property | LFP (LiFePO4) | Lead-Acid (AGM/FLA) | NMC (Li-Ion) |
| Usable DoD | 80–90% | 50% | 80–85% |
| Round-Trip Efficiency | 95–98% | 75–85% | 90–95% |
| Cycle Life | 3,000–10,000 | 400–1,000 | 1,000–2,500 |
| Calendar Life | 10–15 years | 3–5 years | 7–10 years |
| Self-Discharge | 2%/month | 5%/month | 2%/month |
| Weight | ~7 kg/kWh | ~25 kg/kWh | ~6 kg/kWh |
| Installed Cost | $400–$800/kWh | $150–$400/kWh | $500–$900/kWh |
| $/kWh Delivered | $0.06–$0.15 | $0.20–$0.50 | $0.12–$0.25 |
| Charge Below 0°C | ✗ No | ✓ Yes (slow) | ✗ No |
| Maintenance | None | FLA: water topping | None |
| Thermal Safety | Excellent | Good | Moderate |
| Best For | All solar storage | Tight budget, short-term | Compact / lightweight |