Solar Battery Types: Lithium vs AGM vs Lead-Acid
Your battery bank is the most expensive single component in an off-grid solar system — and the one where chemistry choice has the biggest impact on long-term cost, performance, and maintenance. Three main battery types serve the solar market: LiFePO4 (lithium iron phosphate), AGM (absorbent glass mat), and flooded lead-acid.
LiFePO4 (Lithium Iron Phosphate)
The modern standard for solar storage in 2026. LiFePO4 is the chemistry used in residential energy storage systems and many modern EVs, chosen for its safety, stability, and exceptionally long cycle life.
Key specs for a 100Ah 12V LiFePO4 battery:
- Usable capacity: 80–100Ah (80–100% depth of discharge)
- Cycle life: 2,000–6,000+ cycles to 80% capacity
- Round-trip efficiency: 95–98%
- Weight: 24–30 lbs
- Self-discharge: ~2–3% per month
- Built-in BMS: Prevents overcharge, over-discharge, and thermal issues
The one real limitation: most LiFePO4 batteries cannot charge below freezing (32°F / 0°C). Charging below freezing causes lithium plating on the anode, permanently damaging the cells. Quality batteries include BMS protection that blocks cold-temperature charging automatically. Some models (Victron Smart, Battle Born Heated) include internal heating elements.
AGM (Absorbent Glass Mat)
The previous standard — still available and suitable for specific use cases, but increasingly displaced by LiFePO4's falling prices and superior performance.
Key specs for a 100Ah 12V AGM battery:
- Usable capacity: 50Ah (50% depth of discharge for reasonable longevity)
- Cycle life: 300–1,000 cycles to 80% capacity
- Round-trip efficiency: 80–85%
- Weight: 60–70 lbs
- Cold-weather charging: Works below freezing (genuine advantage)
- Maintenance: Sealed, maintenance-free
AGM still makes sense for: rarely-cycled backup systems (less than 20 cycles per year), extremely cold environments without heated battery enclosures, and very tight budgets where upfront cost is the primary constraint.
Flooded Lead-Acid
The cheapest option but requires regular maintenance: checking and topping off water levels monthly, ensuring proper ventilation for hydrogen gas, and using equalization charges. Expect 2–3 year replacement intervals with daily cycling. Only practical as a temporary or extremely budget-constrained solution. Trojan T-105 batteries are the classic choice in this category.
Head-to-Head Comparison
| Factor | LiFePO4 | AGM | Flooded |
|---|---|---|---|
| Usable energy (100Ah) | 960–1,200 Wh | 600 Wh | 600 Wh |
| Cycle life | 2,000–6,000+ | 300–1,000 | 200–800 |
| Efficiency | 95–98% | 80–85% | 75–85% |
| Weight (100Ah) | 25–30 lbs | 60–70 lbs | 60–65 lbs |
| Cold-weather charging | Needs heating below 32°F | Works below freezing | Works below freezing |
| Maintenance | None (BMS handles it) | None (sealed) | Monthly (water levels) |
| Upfront cost | Higher | Lower | Lowest |
| 10-year total cost | Lower (no replacements) | Higher (3–5 replacements) | Highest |
For the direct LiFePO4 vs. AGM comparison, see our Lithium vs AGM comparison.
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