Tarbet Island Battery was built between 1808 and 1814 along similar lines to the other ten coast defence batteries of the Lower Shannon design. While this battery had the usual quadrangle defensive barracks, the gun battery was not the usual fan shape. It is described as being a pentagon or bastion shape with two faces looking out towards the river. Each face had three 24-pdr SB gun, while the salient had a single 24-pdr SB gun. It is thought than this unusual design was to reduce cost by the foundations of earlier batteries. The frontage of the battery was some two hundred feet. It is likely there were also two guns on the roof of the defensible barracks.
The second Tarbet Island Battery was probably built over an earlier battery dating back to about 1783 or possibly the 1790s, two batteries having been built on the Island. The whole site has not been developed as a major power station and all the original batteries have been lost.