From sciencedirect.com

Irreversible Changes of Active Material Caused by Deep Discharge
Deep discharge of batteries often leads to mechanical stresses in the plates, which leads to shedding, poor conductivity, and a diminished lifetime of the system. The active material utilization of a battery is therefore a trade-off against lifetime. Extensive volume changes and crystallographic structure changes during charge and discharge are the most common causes of mechanical stress in battery active materials. In addition, extreme voltages at the end of charge and discharge may initiate unwanted electrode reactions (such as corrosion) and other undesirable reactions (such as gas evolution).