Depth of Discharge Affects Cycling Aging but May Not Affect Real-World Lifetime in Powered Wheelchair Batteries

Powered wheelchairs are essential to many, and lithium-ion batteries are commonly used in powered wheelchairs. This means long-lasting batteries are important for powered wheelchair users to reduce costs and increase sustainability. This study investigates how depth of discharge affects the cycle life of lithium-ion batteries, and what charging strategy maximizes useful battery lifetime for powered wheelchair users under realistic daily usage patterns. Cycling data was obtained from Sandia National Labs and accessed through the Battery Archive database. Full, moderate, and shallow depth of discharge conditions were studied, with temperature and charge rates being held constant. Deeper discharge demonstrated faster fade rates, with shallower depth of discharge surviving many more cycles than deeper depth of discharge. There was a statistically significant difference found between the moderate and shallow discharge fade rates. The full discharge condition had only one cell and demonstrated a pattern of faster fade rate, but this could not be confirmed because only one cell was analyzed. Applying these results to powered wheelchair usage profiles to obtain predicted battery lifetimes from cycling alone demonstrated that the predicted battery lifetimes greatly exceeded what typical usage length would look like. This suggested that calendar aging is a likely competing limitation on battery life compared to depth of discharge, but this comparison was not analyzed directly and future work is needed to confirm this conclusion. Thus, while shallower depth of discharge provides the longest battery life, the practical benefits appear to be limited. Managing factors like storage temperature and state of charge may be more beneficial to extending powered wheelchair battery life.