I turned off my MPPT for several days and let my 100 Ah LiFePO get down to 13.1v with a small load. Turned solar back on and waited until it reached float stage (2+ days later). My MPPT stats say it took 1060 watt-hours to get back to full charge.
Now, I know watts are IxV. However, what should I use as "V" to calculate the total Ah needed to get back to full charge? Actually, the difference between 13.1 and 14.0 is only about 5 Ah (81 VS. 76), but I'm curious.