What makes the arrangement quietly remarkable is its logic: the battery was designed to work in concert with a matching installation directly across the water at Tarbert Island in Kerry. Together, the two positions could lay down a crossfire across the full width of the estuary, effectively closing the river to any hostile vessel attempting to push inland.

The land at Kilkerin was acquired by the government in March 1811, and construction followed shortly afterwards, part of a coordinated programme of defensive works along the Shannon. The battery covers an area roughly 108 metres north to south and 70 metres east to west, enclosed by a drystone moat between four and five metres wide and a substantial rampart. At the eastern end stands a blockhouse, its outer walls battered, meaning they slope outward toward the base to deflect shot and add structural stability. Musket loops at each end of the blockhouse covered the moat, while further loops on the upper level looked inward over the battery's own interior, a precaution against the position being overrun from behind. The doorway was recessed specifically to allow a drawbridge to be raised flush with the wall. Inside, the lower level held storage rooms and a magazine, while the upper floor served as accommodation, lit by a large window at each end. A narrow stair built into the thickness of the wall leads up to the gun platforms. At the centre of the battery's interior sits a small semi-basement vaulted chamber, identified on contemporary plans as a shell-filling room, where artillery rounds would be prepared before being carried to the guns. Kilkerin was not an isolated outpost; on the Clare side alone, companion batteries were established at Kilcredaun near the mouth of the Shannon, at Doonaha some three miles further northeast, and on the southern tip of Scattery Island in the middle of the estuary, with further positions on the Kerry and Limerick shores at Carrig Island, Tarbert, Foynes, and Beagh Castle.