LiFePO4 batteries charge in the same way as lead-acid batteries. There are three stages to this process.
Charge at a Constant Current (CC):
Charge at a constant current (e.g., 0.5C), increasing the voltage continually until it reaches its maximum voltage. (For instance, 14.6V)
Charge at a Constant Voltage (CV):
With a CV charge, the current progressively drops to < 0.05 mA as the voltage remains constant.
Trickle charge is also known as a float charge, but a float charge is not required for LiFePO4 batteries.
Sulphation will occur on the plates of lead-acid batteries if the SOC is not increased to 100 percent. Capacity will be reduced as a result.
However, there is no sulphation in a LiFePO4 battery, therefore charging it to 100% is unnecessary. A LiFePO4 battery can lose electrons when it’s overcharged because too many lithium ions will concentrate at one end of the electrode.
LiFePO4 batteries have a best charge/discharge cycle of 10% to 90%, but in my opinion, a charge/discharge cycle of 5% to 95% is fine.
LiFePO4 batteries should be charged at a rate of no more than 0.5C to avoid overheating, which can have a detrimental effect on the battery. Although your battery’s current limit is 1C or above.
Charging a lead-acid battery under 0.2C is typically accepted as safe.
Voltage Required to Charge
Charge voltage for LiFePO4 batteries should range from 14.0V to 14.6V at 25°C, which equates to approximately 3.50V per cell. 14.4 volts, or 3.60 volts per cell, is the maximum charging voltage that is generally considered to be the best. There is only a small drop in capacity, but you will be able to go through a lot more cycles.
Charging should be promptly stopped if the battery voltage surpasses this level. A protective cut-off feature on your BMS should be avoided at all costs.
No float charging is required for the LiFePO4 battery.
When using a charger that includes a float voltage setting, 13.6V is the suggested value. Then the battery won’t be charged by it.
Temperature of Recharge
LiFePO4 batteries may be charged at temperatures ranging from 0°C to 55°C.
Although it is theoretically permitted to charge below 0°C, it is not recommended. Lithium ions will crystallize at 0°C, lowering the battery’s capacity. So, if you don’t need to charge below 0°C, don’t do it.
Low-temperature LiFePO4 batteries may now be charged at temperatures as low as -10°C, thanks to an upgraded form of battery that has built-in self-heating.
To allow the battery to charge, the BMS raised the temperature inside the battery to 5-10°C.
Low-temperature lithium batteries are also available, although their cycle life is inadequate at -20°C.
Charge in Series
To ensure a high level of battery consistency while using multiple LiFePO4 batteries in series, it is suggested that all batteries be completely charged before connecting them. There may be energy left in other batteries while the circuit shuts down when one battery reaches the high-end or low-end voltage.
Keeping a 50mV (0.05V) voltage difference between the battery and the charger will help increase the battery’s life.