Batteries are electrochemical devices that convert chemical energy into electrical energy. When a battery is considered "dead," it means that it can no longer deliver enough electrical energy to power a device or produce a useful voltage. However, in some cases, a seemingly dead battery may appear to "come back to life" and provide electrical power again, albeit temporarily. This phenomenon can be attributed to several factors:
Recovery of resting voltage: Batteries have an open circuit voltage, also known as resting voltage, which is the voltage measured when no current is being drawn from the battery. When a battery is discharged, its resting voltage drops. However, once the load is removed, the resting voltage may partially recover, making the battery appear to work again. This recovery is temporary, and the battery will eventually return to its depleted state.
Chemical reactions: Batteries operate through chemical reactions between the electrodes and the electrolyte. When a battery is discharged, the reactants are consumed, and the products build up. In some cases, allowing a battery to rest can promote slow, self-reversing chemical reactions that regenerate a small amount of the reactants. This can lead to a temporary increase in the battery's capacity, allowing it to deliver some electrical energy before depleting again.
Internal resistance: Batteries have an internal resistance, which can increase as the battery discharges. This internal resistance can cause a drop in voltage when a load is connected, making the battery appear dead. However, when the load is removed, the internal resistance decreases, and the voltage may recover to some extent. Again, this recovery is temporary, and the battery's capacity remains diminished.
It's important to note that these temporary recoveries are often short-lived, and the battery will eventually return to its depleted state. Repeatedly discharging a battery beyond its recommended limits or relying on these temporary recoveries can have negative effects on battery performance and lifespan. For optimal battery performance, it is advisable to recharge or replace a battery once it has reached its discharge limit.