JHXR2, do you mean this can happen due to electrolyte seeping up around the base of the battery posts? I've never heard of that before but it would make total sense. I learned something. Thanks!
Has to be either electrolyte or hydrogen (which is formed when charging above a certain voltage).
There has to be a seal where the polymer case meets the metal (usually zinc-lead alloy of some kind). There’s not much purchase between the polyethylene case (which doesn’t bond to much), and the terminals. So a bit of over tightening, a bit too much thermal cycling (the terminals will get hot with sustained high current draw), age, vibration, etc. can do it. Couple that with battery ageing, and perhaps some poor control or high ripple, and the potential for more offgas exists.
is the coloration white or green-blue?
I would clean everything with a stiff brush, some baking soda, and then water. I would personally replace the battery, as the likelihood of it happening again is high.
I personally like to wipe the battery case down in pledge to give a silicone coating. I apply dielectric grease or conductive grease (preferred) to everything, but I only leave a practical amount around that terminal to case junction. The rest gets wiped on and wiped off. You don’t want tons sitting in random places either holding off connections or collecting dirt. After all junctions are made I do provide a very light coat over the exposed junction.
If you do clean your old battery and try to use it again, make sure to get a good coat of grease on the terminal-case interface point on the battery. It may help, but if something is compromised, it’s likely to still have issues.
I like using 1/4” drive on battery connections to prevent overtorque and damage of both the terminal On the battery and the connector on the cable which can be easily over tightened, contributing to damage.