Michael Sutton skippers an N47 named Southern Grace. He's also an accomplished marine professional, having operated a yacht management company in Charleston for many years. His response to another owner's post on the Great Harbour Trawler Association's website caught our eye, so we asked Sutton if he would be willing to be an occassional contributor to Trawler Times. This is Sutton's third installment. Read the first two:  Busy Hurricane Season Predicted: Put Your Plan in Writing and Clean Your Bottom or Drag Your A**

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​Why Batteries Explode
 
Port Engine propulsion forward - check,
Port Engine propulsion reverse - check,
Starboard engine propulsion forward - check,
Starboard engine propulsion reverse - check,
Thruster propulsion to Port - KABOOM!

By MICHAEL SUTTON

This was part of a pre-departure check list we were going through while preparing to leave the dock on a Sea Ray 450 Sedan Bridge. What followed the very disturbing BOOM was white smoke billowing out of the blower vents and the large engine compartment hatch which was already open.

After shutting everything down and making sure we were not on fire, the search for the source of the explosion began. It didn't take long to find the thruster batteries completely blown apart. I'm not talking about today's new breed of lithium batteries, just your garden variety lead acid six and 12 volts.

Now you would think with blowers on and the large engine hatch open there would be little opportunity for explosive gases to accumulate. Wrong! The culprit appears to be the combination of a loose ground connection and a gassing battery. The loose ground connection produced the spark when the 400 amp thruster was engaged. The gassing was likely excessive due to the cells being overfilled.

The excessive gassing could have also been caused by a faulty charger or the electrolyte could have been too low in one or more of the cells. In this case however, our investigation found that the other batteries on the yacht had been grossly overfilled and were visibly gassing.
 
Marine batteries are typically under a continuous, regulated charge--by the engine's alternator while underway or by a 110 volt battery charger while on shore power at the dock. In both instances highly explosive hydrogen gas, which can be ignited with the smallest spark, is being produced.

Checking them on a regular basis will help prevent such a serious incident and go a long way in keeping other battery related problems at bay. And when checking or servicing, have respect for the damage and injury a marine battery can inflict. Follow basic safety procedures. Here are some things to consider:

• Wear eye protection.
• Turn off the battery charger and switch before connecting or disconnecting any battery.
• Use insulated tools.
• Never place tools or other objects on top of the battery.
• Remove jewelry from hands, wrists, and neck.
• Always disconnect the negative terminal first and reconnect it last.
• Never smoke around a lead acid battery.
• Ensure there is adequate ventilation to dissipate gasses that vent from the battery when charging.
• Keep the tops of batteries clean and dry.
• Keep cables and connections tight.
• At the first sign of corrosion, thoroughly clean the connection inside and out.
• Keep the battery cells at the proper level using distilled water. Take care not to overfill.
• Do not allow battery electrolyte to mix with salt water. Even small quantities of this combination can produce chlorine gas.
• Watch the gauges for both your engine's alternator and your 110 volt charger for signs of overcharging.

Lead-acid batteries contain a sulfuric acid electrolyte, which is a highly corrosive poison. They produce gasses when recharged and can explode if ignited. There are no shortage of incidents where people have been badly injured and even killed by an exploding battery. When working with batteries exercise caution.

An "exploded view."