I see your point, though we barely ever had to top the tank up with water or salt. The amount of gas created was minimal, at least with our setup - admittedly not as fancy as a battery and a dish of water ;)
I've worked in a rail yard where we overhauled locomotive engine & traction alternator sets, which were generating upwards of 3.3MW so we used a big saltwater resistor as a load bank.
It was the only bit of equipment that scared me, because the plates and tank were fairly rusty. I was waiting for it to let go midway through a test and flood the place with boiling salty water (and who knows what chaos the suddenly unloaded generator would have caused)