1) Battery chemistries: Lead-Acid vs LFP
Lead-Acid (Flooded, AGM/GEL)
- Lowest upfront cost; widely available.
- Prefers shallow cycling; typical design at ~50% DoD for longevity.
- Lower round-trip efficiency; heavier and bulkier.
- Flooded types need watering/venting; AGM/GEL reduce maintenance but still age faster with deep cycles.
Lithium Iron Phosphate (LFP)
- Higher upfront cost; excellent total cost of ownership for daily cycling.
- Commonly supports 80–90% DoD with long cycle life (thousands of cycles).
- High round-trip efficiency and integrated BMS for protection.
- Lighter and more compact—great for homes, cabins, RVs and boats.
2) DoD & usable energy (kWh)
Depth of Discharge (DoD) is how much of a battery you can safely use before recharging. Many lead-acid banks are designed around ~50% DoD; LFP often supports 80–90% while maintaining lifespan.
Size to usable kWh, not nameplate Ah: Usable = Capacity × Allowed DoD × Efficiency. Try your numbers in the Battery Sizing calculator.
3) Cycle life & calendar life
Cycle life is the number of charge/discharge cycles until the battery reaches end-of-life (often 70–80% of original capacity). Typical ranges:
- Lead-acid: ~500–1,500 cycles (depends heavily on DoD and care).
- LFP: ~3,000–6,000+ cycles at moderate DoD and temps.
Calendar life matters too—heat accelerates aging for every chemistry. Keep batteries within recommended temperature bands.
4) Efficiency & charge rates
- Round-trip efficiency: Lead-acid ~80%; LFP ~95% (less energy lost to heat).
- Charge/discharge rates: LFP generally supports higher C-rates; lead-acid prefers slower charging.
- Parasitic loads: Inverters and BMS draw small amounts; account for them when sizing.
5) Charge profiles & BMS
Use chargers/inverters with the correct profile:
- Lead-acid: Bulk → Absorption → Float; avoid long periods partially charged to limit sulfation.
- LFP: Often bulk/absorb with no long float; rely on the BMS to protect from over/under-voltage, temp extremes, and balancing cells.
Never bypass BMS protections on LFP and don’t mix old/new or different chemistries within one series/parallel string.
6) Temperature, storage & safety
- Keep within manufacturer’s charge/discharge temperature limits (LFP typically should not charge below ~0 °C without heating).
- Provide ventilation and clearance per spec; secure batteries against movement.
- For flooded lead-acid, ventilate hydrogen gas; avoid sparks; maintain water levels.
7) Sizing example (worked)
Target 5.0 kWh of usable energy for nighttime loads with ~10% reserve.
- Lead-acid design (50% DoD, 80% efficiency): Required nameplate ≈ 5.0 ÷ (0.50 × 0.80) = 12.5 kWh.
- LFP design (85% DoD, 95% efficiency): Required nameplate ≈ 5.0 ÷ (0.85 × 0.95) ≈ 6.2 kWh.
See your own numbers in Battery Sizing and compare ROI in Solar ROI.
8) Maintenance & warranties
- Lead-acid: Regular checks, equalization (where applicable), and proper charging extend life.
- LFP: Minimal maintenance—follow BMS/inverter settings, keep firmware up to date.
- Warranty: Compare years AND cycle throughput limits; follow installation requirements to stay covered.
9) Which should you choose?
- Occasional backup on a tight budget: Lead-acid can be fine if cycled shallowly and maintained.
- Daily solar storage & long-term savings: LFP’s higher usable DoD, efficiency and cycle life usually win.
- Weight/space constrained (RVs/boats): LFP’s density and safety profile are ideal.
Run Battery Sizing with your nightly kWh, then plug that into Solar ROI to see payback with/without storage.