Originally Posted by Realsquash
Clearly the battery exploded, stuff came out of the inside of the battery. Really there are only 2 ways this happens. A dead short or it got cooked by a "converter" and when boom. I suppose it could have had a good charger and just ran very low on water over time and got hot and popped, too.
Most likely explanation is: Electrolyte level ended up below top of plates (bad) and plates shorted/sparked igniting hydrogen in top of battery case. There's usually 3/4-1" of gap (or more) from the top of the plates to the bottom of the fill caps. Less liquid = more space for hydrogen = bigger boom.
If the charger is output is 13.2 to 13.5 VDC it's good, if it's13.5-14 VDC, it's ok (but may shorten battery life and/or will likely require shorter maintenance intervals). Chances are that battery maintenance was the issue. Charging causes the water in the electrolyte to evaporate, and should (ideally) be topped up with distilled water to keep the levels above the top of the plates. (I couldn't tell if it was a maintenance free battery in the pic)
Definitely a newer "smarter" charger is a good idea. I've had good experiences with the small Xantrex stuff.
Regardless of charger type, keeping an eye on battery electrolyte level is critical, especially if you leave them on constant charge.