There is no doubt that batteries can be dangerous. That is the reason they ALL say to keep in a vented battery compartment and to perform routine maintenance on them. Still, there are certain conditions that are more likely to cause battery explosions.
1) Lithium Ion batteries in general are dangerous. Fortunately for us, they are not commonly sold for Marine use and the ones that are cost so much I sure cannot afford them. I found some for Marine use (12 volt) after watching an advertisement on TV in a fishing show and the cost was like $3000 each. Ya, going to get me a couple of those.
2) Maintenance required batteries need that required maintenance. If they need to have water or electrolyte checked, then do it and do it often.
The lack of maintenance on these batteries tends to cause the electrolyte to "cook off", venting that explosive gas (mostly hydrogen);ready for a spark.
BOOM
3) Do not use non-Marine batteries, even non-marine deep cycle batteries, for Marine use. The biggest reason is that we tend to pound the waves at 20 to 50 miles per hour and never consider what it is doing to our batteries. A battery not designed to take it will crack a case, or short out a plate. A shorted plate heats up, heating the internal electrolytes to a point that they expand, splitting the case. A super hot battery, combined with the hot released gasses now mixing with oxygen in the air, can ignite and explode. Of course, if you boat won't go that fast, and if you provide a cushioned battery box, then I suspect that you can get away with it. I did for many years.
4) Using the wrong battery voltage for a specific use. If you have a 24 volt trolling motor and you loose a battery, you cannot just hook up only one 12V battery and think it will just give you half the operation length. It heats up the battery really fast, and ........ see number 2 above.
Seachaser, I would love to know more about what happened to your batteries. Considering that it was a tractor and a truck, and considering that you have had two explode while most never ever have a battery explode,
well that just has me asking questions. Was it number 2 above that caused the problems?
Bloodhound317, do any of the above possible causes possibly apply to what happened.
One thing is for sure, now is a great time to go out and check our batteries. Are the connections clean and tight (at the very least this makes them last longer)? If they are a maintenance required battery, have you check the electrolyte, have you topped it off? Are we using the correct battery charger for the battery type we have? Does this charger have a limiting switch so it shuts off when the battery is fully charged and helps prevent "cook off"?
Let's learn from Bloodhound317's experience. Batteries tend to be ignored and that is one thing we all probably do to much.