Battery & Cost Tools
Solar Battery Lifespan & 10-Year TCO Calculator
See the true cost of your battery storage over 10 years. Compare Lithium LiFePO4 and Lead-Acid AGM side by side — including replacement cycles, efficiency losses, and cost per kilowatt-hour delivered.
Why TCO Matters More Than Upfront Price
Lead-acid batteries cost significantly less than lithium upfront, but this comparison is misleading. The true cost of ownership over 10 years accounts for:
- Replacement frequency: Lead-acid batteries last 3–5 years in daily cycling; lithium lasts 10–15 years. In 10 years you'll replace lead-acid 2–3 times versus zero replacements for lithium.
- Usable capacity: Lead-acid is only 50% usable (to avoid damage); lithium is 90% usable. You need twice as many lead-acid batteries to get the same usable energy.
- Charging efficiency: Lead-acid loses 15–20% of energy as heat during charging; lithium loses only 2–5%. That difference adds up over thousands of cycles.
- Maintenance: Flooded lead-acid requires regular water top-offs and terminal cleaning. AGM is maintenance-free but still requires careful charging to avoid damage.
Example — 10kWh storage, 10-year comparison:
Lithium LiFePO4: ~$8,000–$12,000 (no replacement needed)
Lead-Acid AGM: ~$3,000–$4,000 upfront × 2–3 replacements = $6,000–$12,000 total
Lithium typically wins at year 6–8 and continues to save money through year 15+
Frequently Asked Questions
Are LiFePO4 batteries worth the extra cost?
For most daily-cycling solar applications, yes. The breakeven point is typically 5–8 years, after which lithium provides pure savings. For occasional-use systems (seasonal cabins, backup power used rarely), lead-acid may be more cost-effective since the batteries aren't cycled often and may last their full calendar life without hitting cycle limits.
What reduces solar battery lifespan the most?
The top causes of premature battery failure are: (1) chronic undercharging — never reaching full charge allows sulfation in lead-acid and cell drift in lithium; (2) overcharging — excessive voltage destroys cell chemistry; (3) excessive heat — every 10°C above 25°C roughly halves lead-acid life; (4) deep discharging below safe limits; (5) high charge/discharge rates beyond the battery's C-rating.
How do I know when my solar batteries need replacing?
Signs include: capacity has dropped 20–30% below original (your system runs out of power sooner than it used to), batteries don't hold full charge for as long, voltage drops quickly under load, or a battery in the bank shows significantly different voltage than others. A battery load tester can confirm remaining capacity.
What is cost per kWh delivered and why is it the best comparison metric?
Cost per kWh delivered = Total cost over life ÷ Total energy delivered over life. It normalizes for different efficiencies, usable capacities, and lifespans into a single comparable number. LiFePO4 typically achieves $0.05–$0.15/kWh delivered over 10 years; lead-acid runs $0.15–$0.40/kWh delivered when accounting for replacements and efficiency losses.