Answer: it is used as an adjective to describe the noun wall.
Step-by-step explanation:
The option that best explains how the bolded participle is used in this sentence is "it is used as an adjective to describe the noun wall".
The word "battered" qualifies the noun "wall". There, it's an adjective. An adjective is used to qualify a noun. Therefore, in this question, the underlined word functions as an adjective as it gives more explanation to the noun which is wall.