Battery explodes! Why?
 

Drove over to check boat in storage when I noticed water under boat. To my surprise it was battery acid dripping from drain. It has a factory installed 3 bank pro charger (3-10 amp banks) and one battery had exploded causing one h*** of a mess. Batteries 1 year old (lead), water level OK 6 weeks ago. Any ideas?

Over charged

Boat is 2012, I would think charger would last longer? And would have fail safe to prevent a overcharge!

This is why I don't leave my charger on over the winter. You just can't trust the monitoring circuits to shut down when fully charged. I manage a large fleet of vehicles, trailers with inverters charges and never leave them on the tenders for fear of either the tenders or batteries causing a fire! I have seen batteries short out and melt down causing extensive heat and acid damage.FWIW

anything that is electrical is prone to failure imo.espically things produced in china.

I always thought there would have to be a spark to cause explosion?

A lead acid bat being charged emits hydrogen. If your not well vented the hydrogen can fill the compartment, then even a marine battery charger can have enough spark to cause ignition. This and also a lot of heat from a bad battery can cause a red hot cable issue.

I use AGM's

I'm not sure of the cause , but I'd be spraying the area down with a baking soda and water mixture to neutralize the acid, then a good freshwater flush afterwards.
Old trick my dad taught me many years ago for cleaning battery cables and terminals.

from what I've seen in the past a battery that becomes low on water level can cause a arc between the lead plates, causing the battery to explode.

If it is left on charge all winter, it needs to be a charger that drops to 0 amps. Very few do. Most charge at a low rate all the time.