Lithium iron phosphate batteries are better charged to 100% than 90%, and should be fully charged at least once a week. This differs from ternary lithium batteries, which are typically charged to 90% as this is the manufacturer's recommended optimal charge level.
As for why it's recommended to fully charge lithium iron phosphate batteries, we have to mention their battery packs. When charging lithium iron phosphate batteries, especially with fast charging, the BMS system, which distributes power among the battery packs, may not work in a timely manner.
The different amounts of electricity allocated to each battery pack will lead to an imbalance between the individual batteries. A battery pack that appears to be fully charged will mislead the entire battery pack into thinking that the batteries are fully charged, when in fact they are not.
The slow charging time at the end of the battery life gives the system enough time to restore the battery balance, so for lithium iron phosphate batteries, it is best to fully charge them each time.
However, it is worth noting that there is a difference between "full charge and discharge" and "overcharge and over-discharge". First of all, it is indeed recommended to "full charge and discharge" for lithium iron phosphate batteries, but this is based on the shallow charge and shallow discharge of ternary lithium batteries.
In other words, lithium iron phosphate batteries can be charged only when the vehicle indicates that the battery is low. If you do not charge the battery when the low battery indicator is displayed, and instead wait until the battery is completely depleted before charging, then it is over-discharged, which will damage the battery.
