Originally Posted by terrencecolp
. My battery had exploded, blowing its top off, the caps off, the cables off, and the door open. This is a regular car battery that would no longer hold a charge that I installed to check my Univolt's operation mainly. It would run a single light for about 3 hours before going completely dead. Mainly like I said I was testing my system before investing in a new battery. Now I don't know if I should install a new battery.
You're lucky you still have a trailer.
Batteries converters and univolts are not magick. Their inner workings are not difficult to understand.
One of the most common ways for batteries to fail is with a shorted cell. Then you end up with a 5 cell battery that has a 10.6 volt float voltage and needs a 12.0 volt charge voltage, in series with a shorted cell that looks an awful lot like an 0.1 ohm resistor.
Charge the battery with any charger -- a Univolt from olden time or the latest fancy newfangled 7 stage charger, and two readily predictable things will happen:
1) The 5 "good" cells will be overcharged because the charger is applying a charge voltage suitable for 6 cells. These cells will then a) run hot and b) gas, that is, emit a mixture of hydrogen and oxygen gas through the vent.
2) The shorted cell, meanwhile, will overheat, because of the resistive heating effects. The electrolyte will eventually boil off (actually boil, not gas) from the heat.
Once that's happened, the temperature of the shorted cell will climb until the ignition temperature of the plastic case is reached. The case then ignites the mixture of hydrogen and oxygen gas. Kaboom.
When a battery has a shorted cell it is also possible for it to catch fire while discharging for the same reason. An explosion is less likely since hydrogen gas is not ordinarily present in any quantity in this scenario.
It is vitally important to check the electrolyte level in flooded cell batteries before charging them and periodically during use. An unusually low electrolyte level in one cell is a sign of trouble and indicates that the battery should be tested. A battery that can't deliver 12 volts under a C/4 to C/2 load (amp hour capacity divided by 4 hours) should be scrapped. A battery that boils electrolyte in one cell during the load test has a shorted cell and should be scrapped.
As for the old Univolt, they're not great but it's unlikely that it contributed to the problem. Even if it has poor output control, a battery in good condition with proper electrolyte levels will not gas enough with overnight charging to reach the point where it could explode.
If you're using an automotive type battery then pry the lids off to see what the electrolyte level actually is. There is less difference between automotive and deep cycle batteries than is generally believed but you still have to watch electrolyte levels.
Frozen batteries -- ones that have been discharged to the point where the freezing point of the electrolyte rises above the ambient temperature -- also explode fairly frequently through a similar mechanism.