Hi, Larry,
Yes, some have reported adding ventilation to the battery compartment. I looked briefly in the KNOWLEDGEBASE (accessed via the C34 Te h Notes page, link at the top of this and all other Forum pages). Sorry, couldn't find it, but Ron Hill wrote a Mainsheet article, with pictures, about twwo adding Nicro vents and drilling through the fiberglass. One high, one low on the forward facing plane of the settee seat just forward of the galley sink.
Many of us who haven't done so (yet?

) have also not reported any "issues" in not adding vents. In reality, very little gas is given off unless your charging system is or goes snafu. I recommend checking charging voltages and amperage as a regular past of the skipper's responsibilities during ANY charging session.