What happens with gas in sealed batterys??

As long as the charge rate is not too grossly above normal the gasses recombine.

This link explains it.

Battry Gasses

My reading of other data is not to exceed 14.4 volts or so. Above this hydrogen forms at the cathode - the negative terminal. Its production will start to destroy the grids inside the battery. Yes, I just read in the above link that the gases will recombine - but the damage has been done. I imagine that if you left your charger on at say 15 volts for several hours you will damage the battery permanently.
Waeco recommend a voltage limiter to be connected in series wth the charger for the fridge. Of course theirs costs an arm and a leg so hit the net. Maybe try a CTek.......W

Hi
First of . do not be mislead by the term "sealed"
They are not fully sealed but are valve regulated
The electrolyte is in a paste form with additives that cause the gases to recombine in normal charging , if the charge rate or voltage is too high the gases do not recombine & are vented via the valves/
correct charging is required for long life
Overcharging will lead to paste drying out & short life
Peter

They are not fully sealed.They are fiitted with a small breather. Some have a short clear plastic tube connected to it.