- At 80% depth of discharge, a 100Ah LiFePO4 gives about 1.0 kWh usable; a 100Ah lead-acid at 50% gives about 0.6 kWh.
- Cycle life is roughly 4,000 cycles at 80% DOD for the listed packs, versus a few hundred for a typical lead-acid deep-cycle battery.
- The charger must have a LiFePO4 profile; equalisation and desulphation modes are not suitable.
- LiFePO4 must not be charged below 0°C. Lead-acid can be, but with reduced life.
1. Usable capacity, not label capacity
Lead-acid is usually cycled to 50% depth of discharge to keep a reasonable life. The listed LiFePO4 packs are designed for 80% DOD. That changes the comparison: a 100Ah LiFePO4 gives about 1.0 kWh usable, while a 100Ah lead-acid gives about 0.6 kWh.
| LiFePO4 100Ah | Lead-acid 100Ah | |
|---|---|---|
| Usable depth of discharge | 80% | 50% typical |
| Usable energy at 12.8V | ≈1.0 kWh | ≈0.6 kWh |
| Cycle life | ≥4,000 @80% DOD | 300–500 typical |
| Weight (typical) | ≈10.3 kg | ≈28–30 kg |
2. Charging is not interchangeable
LiFePO4 needs a charger with a lithium profile. The 12V models are specified at 14.4 ± 0.2V CC/CV. A lead-acid charger with equalisation or desulphation can overcharge the pack; a smart alternator may not hold the right voltage without a DC-DC charger.
Solar is fine with an MPPT controller set to LiFePO4. Do not rely on the BMS to limit charge current; it is a protection device, not a charge controller.
3. Weight and space
A 100Ah LiFePO4 is about 10.3 kg; a comparable lead-acid is closer to 28–30 kg. The weight saving is real, but the case shapes differ: check the terminal layout, hold-down and cable route before ordering.
4. Cold weather
LiFePO4 discharges down to −20 ± 5°C, but charging stops at 0 ± 5°C and resumes at 10 ± 5°C. Lead-acid can be charged below freezing, but its capacity and life suffer. If you charge in winter, plan a heated space or warm the pack first.
5. Upfront cost vs cost per cycle
LiFePO4 costs more upfront. Spread over 4,000 cycles at 80% DOD, the cost per usable kWh-cycle is usually lower than a lead-acid bank replaced every few hundred cycles — but the arithmetic depends on the price you actually pay and how deeply you cycle.
6. When lead-acid still makes sense
If the battery is rarely cycled, sits on a trickle charger, or the system is very price-sensitive and weight does not matter, lead-acid can still be the rational choice. For daily cycling, deep discharge and portable systems, LiFePO4 is usually the better fit.