What is the charge rate (C-rate) of a LiFePO4 battery?
C-rate is charge or discharge current expressed as a fraction of the battery's capacity. 1C on a 100Ah battery is 100A — full in one hour. 0.5C is 50A, two hours. Expion360 LiFePO4 batteries are rated for charging up to 0.5C, with 0.2C recommended for everyday use, and for discharging up to 1C, with 0.5C recommended. Staying inside those numbers protects the cells and is a condition of the 12-year warranty.
What are the charge and discharge rates for Expion360 batteries?
The same C-rates apply across the line; multiply by your battery's amp-hour rating to get amps.
| Rate | Recommended | Maximum | On a 100Ah battery |
|---|---|---|---|
| Charge | 0.2C | 1P | 20A recommended, 50A max |
| Discharge | 0.5C | 1P | 50A recommended, 100A max |
Charge and discharge current by model
| Model | Capacity | Recommended charge (0.2C) | Max charge (1P) | Recommended discharge (0.5P) | Max discharge (1P) |
|---|---|---|---|---|---|
| Group 24 60Ah | 60Ah | 12A | 30A | 30A | 60A |
| Group 24 80Ah | 80Ah | 16A | 40A | 40A | 80A |
| Group 27 100Ah | 100Ah | 20A | 50A | 50A | 100A |
| Group 27 120Ah | 120Ah | 24A | 60A | 60A | 120A |
| GC2 162Ah | 162Ah | 32A | 81A | 81A | 162A |
| EX2 Edge 240Ah | 240Ah | 48A | 120A | 120A | 240A |
| EX1 450Ah | 450Ah | 90A | 225A | 225A | 450A |
How do I calculate C-rate?
Divide the current in amps by the battery's capacity in amp-hours. A 100Ah battery charging at 20A is charging at 0.2C; discharging at 100A is 1C. To go the other way, multiply capacity by the C-rate: a 162Ah GC2 at the recommended 0.2C charge rate is 32A. Time to full or empty is roughly 1 divided by the C-rate, in hours.
480Ah bank (four 120Ah in parallel) × 0.2C = 96A charger.
A 2,000W inverter at 12.8V draws about 165A — that's 1.65C on one 100Ah battery, too much. Two in parallel bring it to 0.8C.
Why does C-rate matter for battery life?
Current creates heat inside the cells, and heat is what ages lithium chemistry. Charging or discharging above the maximum C-rate risks overheating and internal damage, which is why the BMS disconnects when current exceeds its limit. Running at the recommended rate instead of the maximum keeps cell temperature low, which is the single biggest thing you can do to extend the battery's life.
Expion360 recommends 0.2C charging and 0.5C discharging as everyday operating points. The maximums (0.5C charge, 1C discharge) are there for short, heavy loads such as a windlass, a microwave on the inverter or a trolling motor at full thrust.
What is the fastest I can charge a LiFePO4 battery?
Up to 0.5C on an Expion360 battery — a 100Ah battery from empty to full in about two hours at 50A, or a 450Ah EX1 in about two hours at 225A. That is up to three times faster than AGM, which is usually limited to 0.2–0.3C. Make sure the charger, alternator or solar controller can supply that current and is set to a LiFePO4 profile.
Charging is only allowed above 32°F (0°C) on unheated models. VHC™ heated models warm the cells first, then charge, so the full rate is available down to -4°F (-20°C).
What does C-rate mean for solar and alternator charging?
Size the charge source to the bank, not the other way round. A 200Ah bank charges at the recommended 0.2C with 40A, which is roughly 500W of solar through an MPPT controller or a 40A DC-DC charger on the alternator. Most solar arrays and DC-DC chargers deliver 25–50A, well inside the limits, so the practical question is usually whether you have enough charging, not too much.