My car battery was dead when I came back from a two-month trip overseas, so I bought smart chargers for both my cars. According to the Internet, the battery of a car can generate hydrogen gas when being charged. This gas is dangerously explosive if not ventilated properly. Suppose I have two cars parked in the (enclosed) garage of a typical single-family house while I'm away on vacation and leave the smart chargers on - will that be a safety risk? - Michael
Using a smart charger while away shouldn't turn your Hondas into Hindenbergs, experts say.
"I wouldn't be concerned about hooking up one of these chargers and leaving a vehicle for a long period of time," says Garrett Nalepka, automotive professor at Centennial College, in an e-mail. "An acid lead battery can explode under certain conditions - the majority of these are caused by human error or improper use of equipment."
Why do you need to charge your battery if you're not using it?
Your car battery is designed to give you a big enough jolt to start your car - and then recharge as you drive.
Car batteries produce electricity through an electro-chemical reaction. In lead acid car batteries, electricity is produced as ions flow from the lead oxide anode to the metallic lead cathode, through an electrolyte mixture of sulphuric acid and water.
If you apply a current, it reverses the reaction and the battery gets recharged.
Even if your car is parked and you're not using the battery, the reaction keeps happening and it will slowly lose its charge.
Add the power drain from a bunch of accessories - like the alarm system and even the memory settings for the radio, seats and climate control system - and a battery could be completely drained in weeks if nobody is regularly driving the car to recharge it.
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So where does the hydrogen gas come in?
There's hydrogen in that electrolyte mixture, and normally it mostly stays there. Unless it's exposed to a lot of heat, say, from overcharging with a traditional charger - or from having booster cables installed backwards, Nalepka says.
Then you get hydrogen sulphide gas - which is poisonous, flammable and smells like rotten eggs.
"You have to use the correct charge rate for the battery to avoid the chance of overheating it," Nalepka says. "If a battery is charged at a high charging rate or is being overcharged, the electrolyte will start to release the hydrogen - since released hydrogen is flammable, if a spark is provided it can explode."
That spark could come from removing the battery charger cable without turning the charger off, Nalepka says.
If you're home and notice the smell of rotten eggs, "turn off the charger, vent the facility and stay outside until the odour disappears," says Battery University, a site run by Richmond, B.C.-based Cadex Electronics.
But, you can avoid the danger in the first place by using a smart charger, Nalepka says.
Unlike a charger that just delivers a steady current, a smart charger only delivers as much power as your battery needs. Once the battery is fully charged, it will turn off the current.
"The majority of brands of smart chargers will turn themselves off if something is wrong with a battery," Nalepka says. "They can even account for some human error by being able to tell if terminals are hooked up incorrectly."
Charging a battery while you're away with a smart charger "should not pose a fire hazard," says Fire Prevention Canada in an e-mail.
Before you leave
If you're going to be storing your car for a couple of months or longer, consider putting some fuel stabilizer in the gas tank, Nalepka says.
If you don't, the "lighter compounds in the fuel may evaporate and the vehicle may not run very well after the storage period," Nalepka says.
Nalepka also likes to change the oil before storing a car.
"New oil can provide better protection for your engine while in storage," he says. "The additives in the new oil can provide better anti-rust protection to all the engines internal parts."
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