It's an interesting construction to be sure. If it had been a lot of, you would not be bothered by a plural verb.
- A lot of flowers are in bloom right now.
- There are a lot of flowers in bloom right now.
The author seem to be construing an ocean of to be a quantifier that works the same way as a lot of works. That is, it does not change the number any more than words like some or many do.
In English, when there are fractional expressions such as a half of, a part of, a percentage of, a majority of, a third of, etc., the verb agreement depends on the plurality of the nouns that follow them. For example:
50% (A half, A third, A part, etc.) of the university was destroyed by fire. (Not were because university is singular.)
50% (A half, A third, A part, etc.) of the parents were at the meeting. (Not was because parents are plural.)
[Examples are from Subject-Verb Agreement at elc.polyu.edu.hk]
If you change the word back to "back part (of his pants)" or "back half (of his pants)", the two phrases contain the words part and half and the rule applies. Therefore, the verb should agree to pants, not to back.
However, the word side seems trickier than back in "the back of his pants". A pair of glasses has only two sides and if it is the one side of the two sides which is bent, it should use a singular verb as in
The side of my glasses is bent.
Best Answer
While people may translate et cetera in a few different ways, they pretty much all have a similar form: "and so on", "and others", "and so forth", etc.
etc. hasn't been Anglicised in use so as to ignore other features of it's origin, so we generally wouldn't have:
So there isn't much of an argument to be made for treating it any differently to its expanded form. Therefore "the battery etc." is plural.