Can Lead-acid Batteries Be Discharged at Constant Voltage?

Lead-acid batteries, including both flooded and valve-regulated types such as AGM (Absorbent Glass Mat) and gel batteries, are not typically discharged at constant voltage. Instead, they are discharged at a relatively constant current until their voltage drops to a predetermined cutoff level.

During the discharge process, the voltage of a lead-acid battery decreases gradually as the stored chemical energy is converted into electrical energy. This voltage decline is inherent to the chemical reactions occurring within the battery. The rate at which the voltage drops depends on factors such as the discharge current, state of charge, temperature, and battery chemistry.

In many applications, such as in automotive, renewable energy storage, and backup power systems, lead-acid batteries are discharged at a relatively constant current until reaching a specified endpoint voltage. This endpoint voltage is typically determined by the requirements of the application and is chosen to prevent over-discharge, which can damage the battery and reduce its lifespan.

While it’s technically possible to discharge a lead-acid battery at a constant voltage by adjusting the load resistance to maintain a specific voltage level, this is not a common practice due to the nonlinear relationship between voltage and state of charge in lead-acid batteries. Monitoring the battery’s voltage and adjusting the load resistance accordingly to maintain a constant voltage would be complex and impractical compared to simply monitoring the current or state of charge.

In summary, lead-acid batteries are discharged at relatively constant current levels in practical applications, with the voltage dropping gradually over time until reaching a predetermined endpoint voltage. Constant voltage discharge is not a common method for lead-acid batteries due to the nonlinear voltage behavior during discharge.


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