The following is excerpted from https://marinehowto.com/lifepo4-batteries-on-boats/
When reading info on the net that suggest such things such as “13.8V is only 80% SoC for 12V nominal LFP battery“, please do yourself a favor and take this hog wash with a grain of salt. Alternatively, do what we do here in the CMI lab and test these nonsensical claims. An LFP cell will attain 100% SoC at voltages well below 3.6V, if the voltage duration is held long enough, as many lead acid charger do!
Most lead acid designed charge sources can hold the absorption voltage stage more than long enough to cause long term damage or eat into some cycle life capacity of your expensive LFP cells. Some LFP manufacturers are now starting to understand this point, when selling into a lead-acid charger environment, and have reduced recommended max charging voltages accordingly. Of course, some others have not. The quality of the cells used inside the battery also play a major role as to how well they deal with constant voltage being held longer than is necessary.
I recently had four prismatic cells in the shop, sent to me by a gentleman who assumed a GEL setting on his charger was safe. He decided this based on Winston’s voltage specifications. He assumed, seeing as it was only 14.2V or 3.55VPC, and well within the spec, that 14.2V was safe for a nominal 12V bank. However, as I mentioned earlier, voltage is not the only factor to consider. You have voltage, duration at target voltage, and charge rate to also consider.
