Non-rechargeable batteries are often discarded when their voltages cease to support the normal operations of electronic or electrical devices. By connecting a sufficiently large number of used batteries in series, the combined output voltage becomes operable, allowing for further drainage of the residual energy from these batteries. In this study, the discharge behaviors of primary alkaline batteries were characterized. The experimental results showed that batteries connected in series discharged non-uniformly. A "weakest-link" phenomenon was observed in that one battery discharged faster than others until it rendered the entire battery bank inoperable. This unconventional voltage supply required additional circuitries for regulation and/or protection to handle the relatively wide range of output voltage. Nevertheless, the concept of draining the residual energy by stacking up multiple used batteries is feasible. The method prolongs the service life of primary batteries and should lead to applications that benefit economy as well as environment. The potential extensions to this method are also discussed.