My concerns with the submerged battery (SB) and the ice bound battery (IB).
1) SB - If water covered the vents you may have a real problem. You have no idea what the electrolyte status is. Since the sulphuric acid(H3SO4) is in solution with water, when there is a path to a larger vessel with water in it the sulfuric acid will migrate to evenly distribute itself in the entire volume of liquid. Like dropping a shot glass full of salt water into a larger container of fresh water will make everything salty. Less sulfuric acid in the battery will reduce the potential capacity in Amp Hours by the amount of sulfuric acid lost.
2) SB - Pure water is not a very good conductor of heat or electricity. Water with impurities certainly is and could easily have discharged your battery. The more impurities, the better the conduction of heat and electric.
(Easy Example - Microwave a cup of tap water and it boils due to the impurities (minerals) in the water. WARNING - DANGER
Microwave a cup of DISTILLED WATER and IT WILL NOT BOIL. It will become super heated well above 212 degrees F. As soon as it disturbed with ANYTHING that will allow bubbles to form, it will boil explosively
. Myth busters used a sugar cube behind Plexiglas shields. After the cube was dropped into the cup there was NO water in the cup. It had all exploded outwards and burst into high temperature steam.) YouTube - ‪Superheating of water (Mythbusters)‬‏
2) IB - a fully charged battery has all of its sulfuric acid in solution (not deposited on the plates) and has a freezing temperature MUCH lower than water alone. A fully charged battery will not freeze in our world (Arctic Circle excluded).
3) IB - In a battery box surrounded by water that freezes, the danger is that the battery box will not flex enough to prevent the ice from crushing the battery.
Lou and Laura with Bella - German Short Hair Pointer
2008 GMC Sierra 2500HD Crewcab SB Allison Duramax
2010 Flagstaff 8526RLWS - Superglide 3300
HAM CALLSIGN - KC3FFW