DeepDischarge is like starvation and DeepCharging is like overeating.
Deep Charging: Many ordinary BMS allow LiFePo4 batteries to be charged up to 3.9V instead of cutt off ≤ 3.65V. This is called Deep Charging.
Deep Discharge: Similarly discharging ≤ 2.5V is called Deep Discharging. Storing batteries with voltage below 2.5V (52v for a 60v battery) can permanently damage the battery.
Depth of discharge DOD: Charging the battery up to 3.65V and discharging up to 2.5V is 100% DOD.
Cycle: Discharging battery with 100% DOD is called one cycle.
Each time battery is deep charged/discharged it damages the battery anode and cathode and reduces the battery life. Therefore, it is advisable that EV batteries should not be deep discharged or deep charged which means keeping the DOD below 100%
Prevent Deep Charge & Discharge: by charging LiFePo4 batteries up to 3.5v instead of 3.65v and discharging up to 2.85v instead of 2.5v. It is advisable to opt for batteries, which have smart BMS with a Bluetooth app showing correct SOC (state of charge in %). Avoid charging above 90% and discharging below 10%. Some EV companies deliver their vehicles applying this restriction of charge and discharge within desirable limits to meet the warranty commitments.
Range Anxiety: There will be range anxiety with lesser DOD which can be compensated by either charging at the first available opportunity without waiting for battery to discharge fully or buying a larger battery which will benefit by lasting much longer.
Effect of DOD on Cycle Life
The relation between the cycle life and the depth of discharge appears to be logarithmic as shown in the graph. In other words, the number of cycles yielded by a battery goes up exponentially the shallower the DOD. This holds for most cell chemistries.
|50% DOD||5000 cycles.|
|70% DOD||3000 cycles|
|80% DOD||2500 cycles|
**Note: The above figures are indicative only to highlight the effect of DOD on cycle life. They vary as per the type of chemistry and many other factors like temperature and cell balancing.