In 2026 this comparison has a near-verdict: LiFePO4 wins on lifetime economics almost everywhere — 3,000-7,000 cycle life against 300-500 for AGM, 80-100% usable capacity against 50%, half the weight, and no maintenance. A LiFePO4 bank costs 2-3x more on day one and typically 50-70% less per delivered kWh over its life. AGM remains rational in narrow cases: standby float applications (alarm, UPS, gate), extreme-cold unheated installs without low-temp charging protection, and genuinely one-off or short-term builds where the upfront budget is absolute. Everything that cycles regularly belongs on lithium now.
Spec Sheet — LiFePO4 (Lithium Iron Phosphate) vs AGM (Lead-Acid) at a Glance
- Cycle Life: ~3,000-7,000 cycles @ 80% DOD class · ~300-500 cycles @ 50% DOD class
- Usable Capacity: 80-100% of nameplate · ~50% of nameplate recommended
- Weight (100Ah class): ~26-31 lbs · ~60-70 lbs
- Round-Trip Efficiency: ~95-98% · ~80-85%
- Charging: Fast — accepts full charge current to near-full · Slow tail — absorption phase limits acceptance
The Shared Platform: What Both Have in Common
Both are 12V-class deep-cycle battery options for solar, RV, marine, and off-grid use, both are sealed and safe for indoor installation, and both work with mainstream charge controllers and inverters when profiles are set correctly. The comparison is economic and operational, not safety-related.
Side-by-Side Comparison Table
| Specification | LiFePO4 (Lithium Iron Phosphate) | AGM (Lead-Acid) |
|---|---|---|
| Cycle Life | ~3,000-7,000 cycles @ 80% DOD class | ~300-500 cycles @ 50% DOD class |
| Usable Capacity | 80-100% of nameplate | ~50% of nameplate recommended |
| Weight (100Ah class) | ~26-31 lbs | ~60-70 lbs |
| Round-Trip Efficiency | ~95-98% | ~80-85% |
| Charging | Fast — accepts full charge current to near-full | Slow tail — absorption phase limits acceptance |
| Maintenance | None; BMS-managed | None (sealed), but capacity fades with abuse |
| Cold-Weather Charging | BMS low-temp cutoff; heated models available | Charges below freezing (reduced performance) |
| Upfront Cost (100Ah class) | ~$300-950 by brand tier | ~$180-350 |
| 10-Year Cost per kWh Delivered | Baseline (lowest) | Typically 1.5-3x LiFePO4 on cycling duty |
| Best Use Today | Anything that cycles: solar, RV, marine, off-grid | Float/standby duty, unheated cold installs, one-off builds |
The Lifetime Math
A 100Ah AGM at 50% recommended discharge delivers ~640 Wh per cycle times ~400 cycles = ~256 kWh lifetime. A 100Ah LiFePO4 at 80% DOD delivers ~1,024 Wh per cycle times ~4,000 cycles = ~4,096 kWh lifetime — roughly 16x the energy for 2-3x the price. On anything that cycles weekly or more, lithium is not the expensive option; it is the cheap one. AGM's lower sticker price only wins when the battery rarely cycles.
Where AGM Still Belongs
Float and standby duty (alarms, UPS, gate openers) rarely cycles and favors AGM's lower cost and zero low-temperature charging concerns. Unheated installs in hard-freeze climates are AGM's other honest niche: LiFePO4 cannot charge below freezing without heating, while AGM tolerates it. And for a cabin you will visit twice — AGM's lower upfront cost is rational. Everywhere else, the market has already moved: lithium is now the default deep-cycle chemistry.
Quoting this job? We stock LiFePO4 (Lithium Iron Phosphate) products and AGM (Lead-Acid) products at contractor pricing — or get a system quote with both options priced side by side.
Choose LiFePO4 (Lithium Iron Phosphate) If / Choose AGM (Lead-Acid) If
Choose LiFePO4 (Lithium Iron Phosphate) if: the bank cycles regularly — solar storage, RV/marine house banks, off-grid living. The upfront premium repays itself several times over in delivered energy.
Choose AGM (Lead-Acid) if: the application is float/standby, unheated in extreme cold, or genuinely short-term and budget-absolute. AGM remains the honest answer there.
Field takeaway: Cycling duty: LiFePO4, full stop — cheaper per lifetime kWh by a wide margin. Float duty and unheated extreme cold: AGM still earns its place.
Frequently Asked Questions
Is LiFePO4 really cheaper than AGM long-term?
Yes on cycling duty: ~16x the lifetime delivered energy for 2-3x the price means 50-70% lower cost per delivered kWh. AGM only wins where batteries rarely cycle.
Can I replace AGM with LiFePO4 directly?
Usually yes — same 12V form factors — but update charge profiles (LiFePO4 wants ~14.2-14.6V absorption, no equalization) and confirm alternator/converter compatibility. A DC-DC charger is recommended in vehicle installs.
Why can't LiFePO4 charge below freezing?
Charging lithium cells below 0C causes lithium plating, which permanently damages capacity. Quality LiFePO4 batteries include BMS low-temperature charge cutoff; heated models solve it for cold installs. AGM tolerates cold charging at reduced performance.
How much usable capacity do I actually get?
LiFePO4: 80-100% of nameplate routinely. AGM: ~50% recommended to preserve cycle life. A 100Ah lithium effectively replaces a 200Ah AGM.
Is AGM being discontinued?
No — AGM remains the standard for float/standby and starter applications. But for deep-cycle solar and mobile use, the market has shifted decisively to LiFePO4; AGM deep-cycle is now the niche.
Sources & Standards
- PES LiFePO4 battery inventory (portlandiaelectric.supply)
- PES AGM battery inventory (portlandiaelectric.supply)
- Battery University cycle-life data (batteryuniversity.com)
Ready to price your project? Get a free system quote from PES Supply — both options, contractor pricing.
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