LiFePO4 versus AGM: which charges faster under solar conditions?

Understanding Charge Acceptance Rate

LiFePO4 batteries have a higher charge acceptance rate, typically between 1C and 2C, compared to AGM batteries which usually have a charge acceptance rate of 0.5C to 1C. This means LiFePO4 can charge at a rate of 2 to 4 times its capacity in an hour, while AGM batteries can only charge at a rate of 0.5 to 2 times their capacity in an hour. As a result, LiFePO4 batteries can absorb solar power more efficiently and charge faster.

Internal Resistance and Charging Speed

Internal resistance plays a significant role in determining how quickly a battery can charge. LiFePO4 batteries have lower internal resistance compared to AGM batteries. With an internal resistance of around 0.5 mΩ, LiFePO4 batteries can charge faster and hold their charge for a longer period. In contrast, AGM batteries have an internal resistance of around 1.5 mΩ, which slows down the charging process. This difference in internal resistance results in LiFePO4 batteries charging faster under solar conditions.

Real-World Charging Examples

To illustrate the difference in charging speed, let’s consider a scenario where a 12V 200Ah AGM battery and a 12V 200Ah LiFePO4 battery are charged simultaneously under the same solar panel conditions. Assuming the solar panel produces 200W of power, the AGM battery would take around 8 hours to fully charge, while the LiFePO4 battery would take around 4 hours to fully charge. This example demonstrates how LiFePO4 batteries can charge faster and more efficiently under solar conditions.