In grammar, the verb of a sentence refers to the word or words that express the main action that is taking place. As mentioned before, this action can include only a word in the case of present simple and past simple such as the verbs "eat" and "ate", but can also include multiple words especially in the case of perfect or continuous tenses. This implies, in the case of "Some of the banks have been charging higher interest rates" the complete verb is "have been charging" as all these words express the action and are part of a present perfect continuous tense that includes the auxiliary verbs "have been" and the main verb "charging".
