By Jim Kerr

The sun drops below the horizon earlier every day now, and we will soon start driving to work in the mornings in the dark. We may not want to think about it, but a Canadian winter is coming again. In the winter, vehicle batteries must provide maximum power to start our vehicles, while at the same time, their ability to provide that power is restricted by the cold outside temperatures. For example, a battery has only 40% of its cranking power available when the temperature drops to -40C but your engine needs two to three times as much power to crank it over. Ensuring that your battery is fully charged and capable of delivering all its power will help prevent some unpleasant surprises.

A battery is made of a series of plates or grids coated with a lead paste. Slightly different materials are used on the positive and negative plates, and when immersed in an electrolyte (diluted sulphuric acid), electrons build up a charge on the plates. Turn the key and those electrons flow through the cables to the starter and the rest of the electrical system.

In a new, fully charged battery, all the plate material is capable of generating electrons. As a battery ages, the plate material slowly sulphates or hardens and is no longer capable of either holding or producing a charge. Most automotive batteries will last five years before their capacity becomes reduced low enough to cause starting problems. Some batteries will last seven years or even longer, but anything over five years can be considered a bonus.

There are things that will significantly reduce battery life. A loose battery hold down will allow the battery to vibrate and rattle around, cracking the material on the battery plates. This material loosens eventually and falls into the bottom of the battery case. Not only does the battery have less surface area to produce electricity, but that loose material may fall between a negative and positive plate, shorting them out so they no longer work. Good quality batteries are built with special sleeves around the plates to prevent the loose material from bridging two plates.

Leaving your lights on (an easy thing to do at this time of the year) until the battery is dead can damage it. When a battery is discharged, the plate materials begin to harden. Then that portion of the plate won’t accept a charge again. If you do discharge a battery, charge it back up again as soon as possible. A battery engineer once told me that if you discharge a vehicle battery completely only four times, its capacity is so reduced you might as well recycle the battery and buy a new one.

A charging system that is not working correctly can also cause battery damage. Too low a charging rate won’t keep the battery fully charged, so plates start to harden. Too high a charging rate will overheat the battery, speed up chemical reactions, and cause the battery to wear out faster. Today’s computer-controlled charging systems are very good at maintaining charging rates, but they depend on sensing correct battery voltage to do this. A loose or dirty battery connection is seen by the charging system as low battery voltage, so the system tries to charge it up by increasing the charging rate. The dirty posts also prevent the charge from getting into the battery or the battery from sending electricity out to the starter properly.

Fortunately, it is easy to test a battery and the charging system. Almost all automotive repair shops have the equipment. It places a load on the battery while monitoring voltage in the battery. If the voltage drops too low, then it indicates the battery plates are partially sulphated. The battery may work fine to start an engine in the summer but will have difficulty cranking the engine on a cold winter morning. Clean battery cables will help, but when the battery plates have hardened, it is time for a new battery.