What are deep cycle batteries?

Deep cycle or traction batteries are able to discharge to 80% depth of discharge without reducing the cycle life. They can simply be wet flooded batteries, but they adopt thicker and squarer plate grids, which gives them less starting power but more of a constant power supply, helping to resist breakdown and sulphation. However, GEL and AGM batteries have increased deep cycle capability. A deep cycle battery is used for applications that will draw power over an extended period of time.