For the battery with the same specification and the largest number of plates, when the discharge current density is high, the discharge capacity is the smallest; on the contrary, when the discharge current density is small, the discharge capacity increases. This is because when the discharge current density is large, both the electrochemical polarization and the concentration polarization will increase, resulting in a rapid drop in the discharge voltage. The discharge capacity decreases.

    In addition, when the discharge current density is high, the number of lead ions increases rapidly near the electrode, which increases the supersaturation of lead sulfate and forms a thin layer of lead sulfate with fine grains and dense surfaces, which will be too late in the electrolyte. When diffusing into the active material, the pores are blocked, making the active material in the electrode more difficult to react, the utilization rate is lower, and the discharge capacity is lower. Conversely, not only the electrochemical polarization and the concentration polarization decrease when discharging with a lower current density. And because the supersaturation of lead ions is reduced, the resulting lead sulfate layer will be relatively large and loose. Although this salt layer also quickly covers the surface of the electrode, the sulfuric acid electrolyte can still diffuse into the depth of the electrode plate through its pore glands to contact the speech substance, and of course, it can release more capacity. This is also the main reason why for batteries of the same specification, various standards stipulate that less capacity is allowed to be released during high current discharge. For example, for fixed valve-regulated sealed lead-acid batteries, various standards basically stipulate that as long as the 3-hour rate discharge capacity reaches 75% of the 10-hour rate discharge capacity, it will be judged as qualified.