The autonomy of the Samsung Galaxy S21 FE is classic "all-day battery life", i.e. it takes you to the evening, no more and no less, and it does so with a slightly better safety margin than the standard S21 which it is a bit stretched from the first days and becomes a bit "short" when the physiological decrease in battery efficiency begins to become apparent.
The feeling is that, at least at this moment, the S21 FE has a higher baseline consumption than the top-of-the-range S21s, the cause is probably to be shared between the processor (we know that the Snapdragon 888 is not exactly exemplary) and the software still to be optimized properly.
For lovers of numbers we are on about 5 hours of active display, therefore we expected something more but we hope that it will arrive over time, when the S21 FE will also be completely calibrated with updates.