The dry cells are considered single-use cells. Once the electric current given out by the dry cell weakens, it has to be discarded and disposed of. The rechargeable cells or batteries are used multiple times after recharging. The rechargeable cells thus run for longer periods and are preferred over dry cells. However, the rechargeable cells cannot last forever. These also become weak after being used many times, and need to be discarded. Mobile phone batteries need to be changed over time.