Gel and AGM batteries are both sealed lead-acid batteries, but they differ in how the electrolyte is suspended. Gel batteries have thicker electrolytes in gel form, making them better for applications with vibration, while AGM batteries have electrolytes absorbed in a fiberglass mat, providing higher energy density and are commonly used for high-performance or backup power. The best type for an application depends on factors such as power output, discharge rate, size, and operating environment.