There are mounts for two different types of guns at the Lower Battery: One group of four, the other of sixteen. The group of four probably mounted 32-pounder smoothbore guns, and the rest of the mounts? You got me.

Separating the different sections of the battery is an earthen berm, which is what the military calls a pile of dirt. This was to isolate each section from the other, should one of them explode either due to enemy action or the unintended detonation of one of the guns, which was by no means an unusual happenstance.