Battery safety is an issue that knows no seasons. But the frigid temperatures that have paralyzed much of the nation in recent weeks are cause for all service personnel to be watchful for frozen batteries. In the hands of an untrained or careless worker, a frozen battery is a potential bomb waiting to explode. Dealers who haven't seen this calamity should realize that an exploding battery sprays acid and hurls plastic shards. It may cost a worker his eyesight and/or injure people near him-not to mention damage the vehicle!
Why it freezes
You needn't be a chemist or full-fledged technician to understand why batteries explode. Electrolyte, the liquid substance inside a battery, is a mixture of about 40 percent sulfuric acid, about 60 percent water. When the electrolyte reacts with the lead plates inside the battery, chemical energy is converted into electrical energy, pushing electrical current out into the vehicle's electrical system.
Note that hydrogen, a flammable gas, is a normal by-product of the chemical activity inside an automotive battery. More on that in a moment.
Once again, electrolyte is more water than acid under normal conditions. But as the battery discharges or runs down into the state we commonly call a dead battery, the electrolyte becomes almost entirely water.
Below-freezing temperatures can freeze a battery if it goes dead while the vehicle sits for a long time. Other times, the driver gets stuck in deep snow, leaves the flashers on for safety purposes and cannot get back to his vehicle before the battery goes dead and freezes.
Of course, dead batteries are much more likely to freeze in the sub-zero weather that gripped the Midwest and northern states this winter. However, forecasting when a dead battery will freeze is chancy because it varies according to temperature and time-how long the battery was left unattended.
Freezing water expands. That's why ice bursts house pipes and cracks engine blocks in vehicles with insufficient antifreeze.
Likewise, ice inside a frozen battery can crack its case or buckle the lead plates inside it, destroying the battery. Precious few batteries survive frozen electrolyte.
Why it explodes
When someone connects a battery charger to a frozen battery, the charger's electrical energy warms the battery. But unlike the defrost mode on your microwave oven, the charging current isn't likely to warm the battery slowly and evenly.
To the contrary, charging current may boil melted ice into steam inside a localized area of the frozen battery. If this pocket of trapped steam cannot escape, the frozen battery goes off like a hand grenade!
Remember that if a spark manages to enter a battery vent, it'll blow up the battery by igniting the hydrogen normally found above the battery cells. Occasionally, a cracked internal connection above the electrolyte level causes an arc that lights off this hydrogen.
Caution all service personnel not to dally if a battery blows up or a worker somehow splashes himself with electrolyte. One coworker should liberally flush the person's eyes and skin with clean water as quickly as possible while someone else calls for medical assistance.
Assuming that the injured person is being attended to, other workers should rinse any traces of electrolyte from the vehicle because sulfuric acid is extremely caustic.
The tight economy, coupled with dangerously low temperatures, increases the risk of frozen battery-related explosions. That's because Good Samaritan service personnel usually try to fix the vehicle in the most cost-effective manner.
There is a tendency to try charging the battery as soon as possible in hopes of rejuvenating it and getting the vehicle back on the road.
When the temperature drops below freezing, service personnel should watch for visual signs of frozen batteries such as a cracked or bulged-out case or bulged-out vent caps. Instead of skirting the issue, they should advise customers up front that frozen batteries seldom survive.
Always remember to get the vehicle's history. Be wary if it has sat outside with a dead battery during frigid weather.
If you insist on trying to revive a suspect battery, let it thaw overnight inside the shop before attempting to recharge it.
Finally, always wear eye protection when working around batteries.