LiFePO4 vs AGM
AGM (Absorbent Glass Mat) is the most popular sealed lead-acid chemistry. This comparison shows where LiFePO4 pulls ahead and where AGM still makes sense.
Head-to-Head Comparison
| Feature | LiFePO4 | AGM |
|---|---|---|
| Nominal Voltage (per cell) | 3.2V | 2.0V |
| Energy Density (Wh/kg) | 90–160 | 30–40 |
| Cycle Life (80% DoD) | 3,000–5,000 | 400–800 (at 50% DoD) |
| Calendar Life | 10–15 years | 4–7 years |
| DoD Limit | 80–100% | 50% |
| Self-Discharge (per month) | 1–3% | 3–5% |
| Weight (100Ah 12V pack) | ~12 kg | ~32 kg |
| Safety | Thermal runaway >270°C | Sealed, spill-proof |
| Cost per kWh | $250–400 | $150–250 |
| Maintenance | None | None (sealed) |
| Typical Applications | Solar, RV, marine, home backup | Engine start, UPS, mobility, audio |
Pros and Cons
LiFePO4
- + 4–6× more cycles than AGM
- + 60% lighter
- + 80–100% usable capacity
- + Flat voltage curve
- − Higher upfront cost
- − Needs BMS
- − Cold charge limitation
AGM
- + Maintenance-free
- + Spill-proof, any orientation
- + Good high-rate discharge
- + Lower upfront cost
- − 50% DoD limit
- − Heavy
- − Shorter cycle life
Use Cases
Best for LiFePO4
Solar storage, RV house banks, marine deep cycle, home backup, and any application cycling daily. LFP's cycle life advantage makes it the lowest-cost option over 3+ years.
Best for AGM
Engine starting, short-duration UPS backup, mobility scooters, car audio, and applications where upfront cost is critical and cycling is infrequent.
Related Articles
References
BCI Group Size Standards for AGM Starting Batteries, Battery Council International, 2024.
LFP vs Sealed Lead-Acid Cycling Performance — Energy Storage Materials, Vol. 58, 2023.
IEEE 1189-2007 Guide for Selection of Valve-Regulated Lead-Acid Batteries.
Frequently Asked Questions
Is AGM better than flooded lead-acid?
AGM is maintenance-free, spill-proof, and has lower self-discharge than flooded. It handles vibration better and can be mounted in any orientation. However, AGM costs 30–50% more than flooded for the same capacity and still shares the 50% DoD limit of all lead-acid chemistries.
Can AGM and LiFePO4 batteries work together?
No. AGM and LFP have different nominal voltages (2.0V vs 3.2V per cell), different charge curves, and different internal resistance profiles. Connecting them in parallel or series causes uneven charging, reduced efficiency, and accelerated degradation of both banks.
Is AGM good for engine starting?
Yes. AGM batteries excel at high-rate discharge, making them ideal for engine starting (SLI). They recover faster from deep discharge than flooded and are spill-proof, which is critical for engine bay mounting. Many premium starting batteries use AGM construction.
How does AGM cycle life compare to LiFePO4?
AGM delivers 400–800 cycles at 50% DoD. LiFePO4 delivers 3,000–5,000 cycles at 80% DoD. Even comparing at the same DoD, LFP provides 4–6× more cycles. For daily-cycling applications, AGM degrades significantly within 2–3 years.