I have read in a few places, and on one of the USA battery manufacturer's site, that LiFe are not intended for float.
Here is another one I just found:
https://walkingsolar.com/can-you-float-charge-lifepo4/For "float" I mean the old type of simple lead acid DC UPS where the charger takes the load with the battery floating in parallel.
In that case the LA battery floats at 2.25 to 2.3 Volt per cell, and come up to full charge like that. eg 13.8 Volt
So power failure has the full capacity available eg 85 A.h. Battery can run like that for years with occasional outages.
The telepower and power generation station UPS that I worked on in the past had Lead Acid battery life of 20+ years
If trying to do that with LiFe, there are 3 problems ( as I read):
1) The charge voltage to get full charge into battery needs to be about 14.5 V or more.
If floating at 13.8 V, the battery will only charge to about half capacity approx.
2) But Floating a LiFe continuously at 14.5 V +, causes chemical erosion problem as described in some sites.
3) To purchase a reasonable quality retail #27 battery, 85 A.hr cost me ~ $120 inluding core, expect 4 years+
When I compared reasonable quality LiFe, the same 85 A.h considering the reduced capacity would have cost more than $800.
I looked at options of smaller 12V batteries in parallel or a single large one, and both cost more than $800.
And while the LiFe lifetime is better than Lead Acid for number of discharges,that does not matter much in a UPS.