Battery case top explodes

[Robert H. Wilkinson]

Ron, as others have said - if you were anywhere near the boat at the time you would have heard it! Also cleanup is important, if there was any acid spill the compartment should be flushed with lots of water and baking soda(neutralizes acid). Once a battery starts to boil it is producing hydrogen gas(highly explosive). This gas as well as the liquid acid can do a lot of damage to wiring, electrical/electronic equipment in the area. Sometimes the damage will manifest itself months later. So it is important to neutralize and flush.

You noted in your last post that the electrolyte level was low. Once it drops below the level of the plates it can lead to plate deformation - which can lead to internal shorting.

I'm not sure how the 4 batteries on your boat are configured, but sometimes in multiple battery banks - if one battery becomes defective - the other one will overcharge - causing excessive gassing - creating a potentially dangerous situation - and eventually the demise of both batteries. This does not mean your charger is faulty. Any batteries in the same bank should be replaced together. They should also be the same type and capacity. If 2 batteries of different capacities are charged together one will be undercharged and the other can be overcharged.

Regards, Rob