At a high state of charge, the battery operates at a higher voltage, which can increase stress on the battery's internal components. Keeping a battery at high charge levels for prolonged periods can accelerate unwanted side reactions in the battery, leading to the formation of a solid electrolyte interphase (SEI) layer on the anode. While some SEI formation is normal, excessive growth can impede battery performance and capacity.

Likewise, at a low state of charge, the voltage is lower, which can also stress the battery and lead to degradation of the cell's structure. Allowing a battery to remain at very low charge levels can lead to increased internal resistance and potential for electrolyte decomposition, both of which degrade the battery’s capacity over time.