Elon Musk says that Tesla's Model 3 and Model Y vehicles with iron phosphate LFP batteries can be safely charged to 100% and, in fact, it is even recommended for better range estimation. It seems that said range can be underestimated by tens of miles, too, as one Model 3 experiment showed.https://www.notebookcheck.net/Tesla-Model-3-pulls-35-miles-of-extra-range-after-its-LFP-battery-charge-display-drops-to-zero.660061.0.html
Buffer was 7kwh. BMS was misaligned so don't take that value as real for any M3.