How LFP Prismatic loses capacity
LFP fades slowly and fairly linearly for most of its life. Capacity loss is driven mainly by lithium inventory being locked up in the SEI layer on the graphite anode, while the cathode structure stays largely intact.
At about 160 Wh/kg and a nominal 3.2 V per cell, LFP Prismatic sits in a specific trade-off between energy density and durability that shapes how it ages in service.
Finding the knee before it finds you
The knee — the point where fade accelerates — usually arrives late, often well past the point a vehicle retires the pack. That is why most retired LFP packs still test in grade A or B territory.
The practical test is trend rather than a single reading: a module whose resistance is rising faster than its neighbours is heading for the knee, even if its capacity still looks healthy today.
| Measured SOH | Grade | Typical route |
|---|---|---|
| 85% and above | A | Grid-tied or commercial storage |
| 75–85% | B | Telecom backup, solar buffering |
| 65–75% | C | Low-duty backup, short warranty |
| Below 65% | D | Discharge and refining |
Signals worth tracking in the field
Fleet telematics can flag packs that are ageing faster than the rest of the fleet long before they retire. Pairing that data with a bench test at retirement makes grading faster and pricing more accurate.
- Usable capacity at a standard rate and temperature
- DC internal resistance per module
- Impedance spectrum shape from EIS sweeps
- Self-discharge over a rest period
- Temperature history and fast-charge share