Expect the precautions for using LFP battery cells to be refined as more experience is gained. In considering whether or not to use LFP instead of LA batteries, take the following precautions:
- Never overcharge LFP batteries—even a fraction of an hour of overcharging can permanently damage the cells. A battery management system (BMS) is essential to preventing overcharging.
- Never short LFP batteries! LFP batteries can put out even more instantaneous current than LA. When working around any batteries, always use insulated tools.
- Don’t place LFP batteries upside-down (any other orientation is OK). If upside down, electrolyte can leak out of their safety vents if the batteries become overheated.
- When creating a series pack, use cells from the same manufacturer, and the same model and age, so they are as closely matched as possible. This is the same for LA batteries. You won’t be able to get LFP cells perfectly matched, and that is another reason why a BMS is needed.
- To increase capacity, it is preferable to use a single string of larger cells rather than paralleling smaller cells. The weaker of the paralleled cells will reduce the overall efficiency of the pack. For this same reason, LA batteries also have better performance when not in parallel. If paralleling is unavoidable, then only well-matched cells (make, model, age, capacity, impedance) should be paralleled.
- Reduce the charging current for LFPs to a C/10 or less when the cell temperature is below 32°F. Otherwise, permanent damage to the cell may result. Check with the manufacturer for specific temperature and current limits.
- Long-term trickle or float charging is not LFPs’ optimum use. LFPs have the best price/lifetime energy payback when cycled often. If floating is unavoidable, then caution must be used to select a safe yet effective float voltage.
- Store LFP battery cells at a 40% to 60% SOC to optimize their shelf life. Storing them at 0% SOC is likely to permanently damage them, and storing them at 100% SOC may reduce their cycle life.
- With only 12 years of history, the battery industry is still learning the optimum way to treat LFP batteries (e.g., some say charging to 80% rather than 100% will greatly increase cycle life).