LiFePO4 vs NMC vs lead-acid
The comparison that matters is not energy density on a datasheet. It is cost per usable kilowatt-hour over the life of the system, which depends on depth of discharge, cycle life and how the chemistry behaves at the temperature it will actually see.
Start from usable energy, not rated capacity
A 100 Ah lead-acid battery is normally cycled to 50 % depth of discharge to reach its rated life, so it delivers about 50 Ah usefully. A LiFePO4 pack of the same rating is designed for 80–90 % depth of discharge and delivers 80–90 Ah. The lead-acid pack therefore costs roughly twice what its label suggests for a given amount of usable energy.
| Lead-acid | LiFePO4 | NMC | |
|---|---|---|---|
| Usable energy per rated kWh | ~50 % | 80–90 % | 80–90 % |
| Cycle life at that depth | 300–500 | 3,000–6,000 | 1,000–2,000 |
| Mass per usable kWh | baseline | ~1/3 | ~1/4 |
| Thermal stability | n/a | High | Lower |
| Cost per usable kWh, first purchase | Low | 2–3× lead-acid | 1.5–2× LiFePO4 |
| Cost per usable kWh, ten-year | High | Lowest | Middle |
Where NMC still wins
NMC has higher energy density and better low-temperature performance. That makes it the right choice for applications where mass or volume is critical — some portable equipment, certain electric vehicles — and for cold-climate use where LiFePO4's restricted charging below 0 °C is a real limitation.
It is not the right choice for stationary storage, where mass is irrelevant, the cost per kilowatt-hour is the deciding factor, and the additional thermal stability of LiFePO4 is worth having in an installation that may be in a building.
Where lead-acid is still correct
Being honest about this matters more than defending a chemistry. Lead-acid remains the sensible choice where:
- Capital cost is the binding constraint and the application is light duty — a standby battery that discharges twice a year does not benefit from 6,000 cycles.
- The installation is genuinely temporary. A project battery that will be scrapped in two years does not benefit from a ten-year service life.
- Weight and space are abundant and there is no benefit to the size reduction.
Where any of those change — duty cycle rises, the installation becomes permanent, space becomes constrained — the calculation usually shifts to lithium.
The temperature question
LiFePO4 must not be charged below 0 °C; charging at lower temperatures causes permanent lithium plating. Discharge is permitted to -20 °C or lower depending on the specification.
Lead-acid tolerates charging when cold but loses capacity, and its life halves for roughly every 10 °C above 25 °C — which is why lead-acid in a hot cabinet fails years before its rated life.
For cold installations with LiFePO4, specify low-temperature charge cut-off and, where charging must continue, internal heating. Claiming the chemistry "works in the cold" without that provision is how packs come back.