Back when I first started using an electric trolling motor, I first started using a battery charger. Never had to use one before, just never came up. So the first time I used my new charger on my new deep cycle battery, I had it set up on my front porch, attached the cables, plugged it in, and went in to clean the fish. Suddenly, the sound of seven shotguns rattles the neighborhood and my windows, and I run out to see that my battery is in a hundred pieces around my porch and driveway. Everybody along our street is on their porch looking over at me wondering what the explosion was, and I'm in shock, thanking my lucky stars that our dog was in the house, and nobody was near that thing when it blew. I got all the pieces picked up and cleaned up and all that. The next day I realized one thing I shouldn't have forgotten: All that battery acid had splattered all over the porch AND MY TRUCK, and I didn't hose anything off. My paintjob was ruined by a thousand little black pockmarks, both on the truck and the house. ARRRRGGG!!!!
I think the reason it exploded was that I didn't pop the caps off the battery.
Now it's the first thing I do.