LiFePO4 batteries: the practical buyer's guide
Lithium iron phosphate (LiFePO4 or LFP) has become the default chemistry for RVs, vans, boats, off-grid homes, power stations and a growing share of EVs. It trades a little energy density for long life, thermal stability and usable capacity that lead-acid cannot match.
The numbers that matter
| Property | LiFePO4 | AGM lead-acid | NMC lithium |
|---|---|---|---|
| Nominal cell voltage | 3.2 V (12.8 V for 4 cells) | 2.0 V (12 V for 6 cells) | ~3.6–3.7 V |
| Practical usable depth | 80–100% (we default to 90%) | ~50% for good life | ~80–90% |
| Typical cycle life | Thousands of cycles | Hundreds of cycles | Around 1,000–2,000 |
| Weight for same usable energy | Light | Heavy (2–3×) | Lightest |
| Thermal stability | Very good | Good | Moderate |
| Charging below 0 °C | Not allowed without heating | Allowed (slower) | Not recommended |
Cycle-life claims depend heavily on depth of discharge, temperature and charge rate; compare warranties in years and cycles or MWh throughput.
Voltage and state of charge
LiFePO4 has a very flat voltage curve: a 12.8 V battery sits around 13.2–13.3 V for most of its range. That makes voltage a poor fuel gauge. Use a shunt-based battery monitor or the BMS's Bluetooth readout to track state of charge in amp-hours or percent.
Typical charge settings for a 12.8 V pack are around 14.2–14.6 V absorption with a low or no float. Always follow the battery maker's specification sheet — not a generic preset on your charger.
What the BMS does
Every lithium battery needs a battery management system. A good BMS protects against over-voltage, under-voltage, over-current, short circuit and temperature extremes, and balances cells so they stay matched. When comparing batteries, look for:
- Continuous and peak current ratings that exceed your inverter's draw
- Low-temperature charge cut-off, or a built-in heater for cold climates
- Communication (CAN/RS485/Bluetooth) if your inverter can use it
- Clear limits on how many batteries can be connected in series or parallel
Sizing a bank
Add up daily watt-hours, multiply by the days of autonomy you want, divide by inverter efficiency and usable depth of discharge. Our battery bank sizer does this and warns you when your system voltage is too low for the current involved. For a portable power station, use the runtime calculator.
Series, parallel and system voltage
Batteries in series add voltage (two 12.8 V make 25.6 V); in parallel they add capacity. Higher system voltage reduces current, cable size and losses — a 3,000 W inverter draws about 250 A at 12 V but about 63 A at 48 V. Read 12 V vs 24 V vs 48 V before buying.
Installation and safety
- Fuse the positive conductor as close to the battery as possible with a fuse rated for the battery's short-circuit current (Class T is common on larger lithium banks).
- Torque terminals to the manufacturer's specification; loose lugs cause heat.
- Keep cable lengths in a parallel bank equal so batteries share current evenly.
- Mount securely in vehicles and boats; keep away from ignition sources and water.