Part of the thread on a battery install under the kitchen cabinet on a Westy
prompts this question: Is venting of a modern non-sealed battery really
necessary?
This is my understanding of the construction of most of the batteries on the
market today, those that are marked "No Maintenance" or some such label.
Instead of the old screw in plugs, one in each cell of the battery, modern
batteries seem to have a plastic plate covering the top of the battery with
a plug for the hole into each cell.  Sometimes one plate, sometimes two.
These can be pried off to check the level of the electrolyte in each cell.
But my understanding is that these plug/covers are constructed so that any
vapor coming from the battery condenses and runs back into the battery.  But
any actual gas, like hydrogen, is vented.  And I know that at least some of
such batteries have a little nipple that can be attached to a small hose
that leads outside the battery compartment thus venting something.
So this leads to the question "What happens when such a battery is NOT in a
sealed compartment and is NOT vented outside the vehicle?"
Is there any potentially toxic 'stuff' coming into the vehicle? Is there a
danger of corrosion in the immediate area of the battery? Or is the venting
of a modern battery a non issue for installing under the kitchen or under
the rear seat without a sealed battery compartment?
BTW, I'm assuming normal use and charging of the battery, no severe over
charging or over heating of the battery that you would expect boiling of the
electrolyte or catastrophic failure of the battery case.  That's a whole
different problem for any battery, sealed or not.