Depth of discharge (DOD)
All battery manufacturers recommend to keep the Depth of Discharge (DOD) bellow the maximal limit of 100%. Ideally 80% DOD or less is recommended. The rule is quite simple: the smaller DOD the larger number of cycles. With 50% DOD the LiFePO4 cells may have well above 5000 cycles. However it is imporatnt to keep the DOD at the cetral part of the capacity range. If the DOD is not in the center of the capacity range, the cell performace may degrade faster.
As a matter of fact, since it is better to avoid deep cycle discharging, it seems to be better to charge as frequently as possible. It is better to “charge (to full) and drive” rather than “drive and charge (from null)”.