I needed to replace the house battery aboard our boat this weekend. The house and starter battery are in a fiberglass battery box that is accessible through an access hatch in the cockpit floor, under a removable teak floor grate.
I pulled the dead house battery and good starter battery out of the battery box, cleaned the box out, put the new house battery in, put the good starter battery back in, and hooked the wiring back up. Then I shut the port in the cockpit floor, replaced the teak grate, and went into the cabin to turn on the main battery selector switch. The switch would not turn.
While standing with my hand still on the switch, I started hearing popping/hissing noises. It took about 5 seconds to determine it was coming from the general vicinity of the battery box. I pulled out the floor grate, lifted up the hatch panel, and saw that what had been a perfectly good starter battery was on fire, with flames and a cloud of smoke and battery acid spewing from the top of it.
Nothing, and I mean nothing, will raise your heart rate like seeing unexpected flames coming out of your boat.
5 seconds later, I was standing in the companionway directing a fire extinguisher into the battery box and neighboring engine compartment. Every time I stopped spraying the fire extenguisher, the battery would catch fire again. Worried I'd run out of fire extinguishers before the battery depleted its charge, I used a pair of insulated diagonal cutters to cut the lead to the battery.
I've included a picture of the battery afterward. After the smoke cleared, where the terminal used to be on the left of the battery was a melted hole in the battery case. I did not realize how much acid escaped the battery until I sprinkled baking soda into the battery box and saw it reacting to neutralize the acid. The insulation was melted off of much of the wiring in the battery box. Every surface in the engine compartment was coated with material from the fire extinguisher. I am lucky that is all the damage there was.
It appears that between removing and reinstalling the starter battery from the battery box, I somehow turned it around so that when I re-wired it, the positive and negative terminals were reversed. This was an easily avoidable mistake--I should have double-checked the terminals before connecting the wires.
I am posting this here not for advice (I'm fully aware of what mistake I made), but as a reminder that 12 volt batteries can be dangerous if not wired correctly. Also, it is prudent to have a fire extinguisher and a pair of insulated wire cutters at the ready when doing any work involving the batteries.
I pulled the dead house battery and good starter battery out of the battery box, cleaned the box out, put the new house battery in, put the good starter battery back in, and hooked the wiring back up. Then I shut the port in the cockpit floor, replaced the teak grate, and went into the cabin to turn on the main battery selector switch. The switch would not turn.
While standing with my hand still on the switch, I started hearing popping/hissing noises. It took about 5 seconds to determine it was coming from the general vicinity of the battery box. I pulled out the floor grate, lifted up the hatch panel, and saw that what had been a perfectly good starter battery was on fire, with flames and a cloud of smoke and battery acid spewing from the top of it.
Nothing, and I mean nothing, will raise your heart rate like seeing unexpected flames coming out of your boat.
5 seconds later, I was standing in the companionway directing a fire extinguisher into the battery box and neighboring engine compartment. Every time I stopped spraying the fire extenguisher, the battery would catch fire again. Worried I'd run out of fire extinguishers before the battery depleted its charge, I used a pair of insulated diagonal cutters to cut the lead to the battery.
I've included a picture of the battery afterward. After the smoke cleared, where the terminal used to be on the left of the battery was a melted hole in the battery case. I did not realize how much acid escaped the battery until I sprinkled baking soda into the battery box and saw it reacting to neutralize the acid. The insulation was melted off of much of the wiring in the battery box. Every surface in the engine compartment was coated with material from the fire extinguisher. I am lucky that is all the damage there was.
It appears that between removing and reinstalling the starter battery from the battery box, I somehow turned it around so that when I re-wired it, the positive and negative terminals were reversed. This was an easily avoidable mistake--I should have double-checked the terminals before connecting the wires.
I am posting this here not for advice (I'm fully aware of what mistake I made), but as a reminder that 12 volt batteries can be dangerous if not wired correctly. Also, it is prudent to have a fire extinguisher and a pair of insulated wire cutters at the ready when doing any work involving the batteries.
