Lithium vs AGM vs Lead-Acid Batteries for Solar
- LiFePO4 has the lowest cost per cycle of any battery type — cheaper than AGM over a 10-year period despite higher upfront cost.
- AGM is a good budget starting point but plan to replace every 3–5 years.
- Flooded lead-acid requires maintenance (water topping) but offers the lowest upfront cost.
- LiFePO4 is lighter, safer, charges faster and tolerates partial state of charge better than any lead-acid type.
- For any new permanent installation in 2026, LiFePO4 is the right choice.
Quick comparison
| Feature | LiFePO4 | AGM | Flooded Lead-Acid | Gel |
|---|---|---|---|---|
| Cycle life (at rated DoD) | 3,000–6,000 | 500–800 | 1,000–1,500 | 500–1,000 |
| Recommended DoD | 80% | 50% | 40–50% | 50% |
| Usable from 100Ah | 80Ah | 50Ah | 40–50Ah | 50Ah |
| Weight (100Ah 12V) | ~13 kg | ~28 kg | ~30 kg | ~28 kg |
| Charge efficiency | 98–99% | 85–90% | 80–85% | 85–90% |
| Self-discharge/month | 1–3% | 3–5% | 5–15% | 3–5% |
| Maintenance required | None | None | Yes (water) | None |
| Price (100Ah 12V) | $250–$400 | $120–$200 | $80–$150 | $130–$220 |
The real cost: cost per cycle
Upfront price is misleading. The true cost of a battery is its price divided by its total usable cycle life. Over 10 years, LiFePO4 is almost always cheaper:
| LiFePO4 | AGM | Flooded LA | |
|---|---|---|---|
| Purchase price (10kWh bank) | $5,500 | $2,000 | $1,200 |
| Replacements in 10 years | 0 | 2–3× | 1–2× |
| Total cost over 10 years | $5,500 | $6,000–$8,000 | $2,400–$3,600 |
| Cost per usable kWh-cycle | ~$0.15 | ~$0.50 | ~$0.30 |
| Winner | ✓ |
LiFePO4 in depth
Lithium iron phosphate is a specific lithium chemistry chosen for off-grid solar because of its exceptional safety profile. Unlike the NMC or NCA lithium batteries in laptops and electric vehicles, LiFePO4 does not undergo thermal runaway — it will not catch fire or explode even if punctured, overcharged or short-circuited.
- Pros: Longest cycle life, highest DoD, lightest weight, fastest charge acceptance, no maintenance, tolerates partial state of charge, no off-gassing
- Cons: Highest upfront cost, cannot be charged below 32°F (0°C) without heating, requires a BMS
- Best for: Any permanent installation, mobile systems where weight matters, cold climates (with self-heating models)
AGM in depth
Absorbed Glass Mat batteries are sealed lead-acid batteries where the electrolyte is absorbed into fibreglass mats. They're maintenance-free, can be mounted in any orientation and don't off-gas under normal conditions. The most common upgrade from flooded lead-acid.
- Pros: No maintenance, sealed (no off-gassing), widely available, established technology, lower upfront cost than LiFePO4
- Cons: Short cycle life (500–800 cycles), heavy, sensitive to over-discharge, slow charge acceptance at high states of charge
- Best for: Budget builds where upfront cost is the constraint, temporary installations, backup systems used infrequently
Flooded lead-acid in depth
Traditional flooded lead-acid batteries (like golf cart batteries) are the oldest and cheapest option. They require periodic water top-ups and must be installed in a ventilated space due to hydrogen gas off-gassing during charging.
- Pros: Lowest upfront cost, longer cycle life than AGM, easily recyclable, widely available
- Cons: Requires maintenance, off-gasses hydrogen (ventilation required), heavy, sensitive to over-discharge and freezing
- Best for: Very tight budgets, stationary installations with good ventilation, situations where replacement is easy and cheap
Cold weather performance
| Temperature | LiFePO4 | AGM | Flooded LA |
|---|---|---|---|
| 25°C (77°F) | 100% capacity | 100% capacity | 100% capacity |
| 0°C (32°F) | 80–90% capacity* | 70–80% capacity | 60–70% capacity |
| −20°C (−4°F) | Cannot charge* | 30–50% capacity | 20–40% capacity |
*Self-heating LiFePO4 models resolve the charging restriction below 0°C.
Which should you choose?
Frequently asked questions
Can I replace my AGM batteries with LiFePO4 without changing anything else?
Usually yes, with one important check: your charge controller must support a LiFePO4 charge profile (different absorption and float voltages than lead-acid). Most modern MPPT controllers do. See our MPPT controller guide for compatibility.
Are cheap LiFePO4 batteries from Amazon safe?
Stick to known brands — Renogy, SOK, Ampere Time, Battle Born. Unknown brands may use Grade B or C cells with inadequate BMS protection. A failed BMS in a lithium battery is a fire risk. The price difference is not worth the safety risk. See our LiFePO4 battery guide.
What's the best battery for a van or RV?
LiFePO4 without question for mobile applications — the weight saving alone justifies it (LiFePO4 weighs 40–60% less than equivalent AGM). In a van, 200Ah of LiFePO4 weighs ~26 kg vs ~56 kg for AGM. See our van solar guide.