SLI batteries are also often called starter batteries. The internal design is comparable to deep cycle batteries with a few important differences. Both types of batteries use lead plates. However, SLI batteries use thinner plates with lead dioxide materials.
The typical SLI battery includes six galvanic cells to provide 12 volts of power. Each cell contains a series of lead and lead dioxide plates immersed in an electrolyte solution. The electrolyte reacts with the lead dioxide plate to create ions and lead sulfate. The chemical reaction produces electrons that pass through the battery terminals as electricity.
The thinner plates provide more surface area, which is needed to produce higher currents. You get a lot of power at once, but with a faster rate of discharge compared to deep cycle batteries. If the battery is fully discharged, the plates may become damaged, which is why SLI batteries go through continuous cycles of charge and discharge.