Should I buy a battery charger?

By Stuart Johnston

Most motorists will be able to get by without a battery charger, as cars are designed to recharge batteries as soon as the engine is running. But if your car stands idle for long periods of time, buying a battery charger can save you a lot of hassle, and increase the life of your battery.

There are reasons for this and they lie in the design and construction of a typical lead-acid battery, which is the energy-storage device fitted to most motor cars.

How does a car battery work?

The lead-acid batteries fitted to 99 per cent of cars running around the suburbs and highways follow a design that has been in place for over 100 years. These days most cars use a 12-volt battery, with the electrics designed to operate with a 12-volt system. Some old cars, notable VW Beetles built before 1966, operate on a 6-volt battery system. Many of these older Beetles were retro-converted to the more efficient 12-volt system.

A typical 12-volt battery consists of six-rows of lead plates contained within the plastic battery casing. Each of these six rows comprises two plates placed side-by side, but separated by an insulator. There is a positive plate and a negative plate. The positive plate is coated with lead dioxide and the negative plate is made of sponge lead. These plates are submerged in a solution of water and sulphuric acid. The final stage of battery construction is to infuse this solution with an electrical charge, for a combined total of just over 12 volts

A battery is constantly being charged and discharged over its lifespan

Just like your cell-phone battery,  a car battery is constantly being charged and discharged over its lifespan. Discharging occurs when the starter motor is cranked to get the engine running, and this is the biggest drain on a battery. Switching on the lights and other electrical equipment also has a discharging effect on a battery.

How is the battery re-charged?

Once the engine is running, there is a belt-driven device called an alternator that is connected to the battery and re-charges the battery. In normal operation, if the car is used over a fair distance each day, this is sufficient to recharge the battery fully, so that there is more than enough “juice” to start the car again.

But if you don’t drive your car often, the battery can be drained to low levels

An alternator on a car recharges a battery quite slowly. So if you are doing short runs in your car and leaving it to stand idle for, say, a week or two at a time, the basic charge in the battery will drop off.

Immobilisers and alarms will drain a battery over a period of a few weeks

A car left standing will often show blinking lights on the dashboard, indicating that an immobiliser or alarm is drawing current from the battery.  After a week or two this can completely drain a battery. And if a battery is drained below a certain level, the plates become coated with sulphate crystals that are not restored when the battery is recharged, and this will eventually make the battery impossible to recharge. So, if your car stands idle for long periods, you need a battery charger.

Battery chargers generally cost between R350 and R1 000 for a reasonable charger that can safely be used in a home environment.

But buy a battery charger that automatically stops charging, once the battery is charged

A note of caution here is to buy a battery charger that automatically reduces the amount of charge as the battery is re-charged, and then stops charging it once the battery is fully charged. Check with your spares shop salesman on the various attributes of a battery charger you are considering.

Overcharging can be dangerous

There have been many reported cases of overcharged batteries exploding. So our advice is to firstly buy a battery charger with an automatic switch-off device. And secondly, monitor the charging of your battery. It is safer to manually check the battery charging via the meter on the battery charger, rather than just plugging in the charger and leaving to its own devices.

 A typical re-charge will take between 12 and 24 hours, using a trickle charge setting. Full charge settings are available on most battery chargers, if you need a quick re-charge after running your battery flat by, for instance, leaving the car lights on overnight. But don’t leave the charger on a full-charge setting for long periods.

We recommend removing the battery before charging

Battery chargers can be safely hooked up to a battery that is still installed in the car’s engine bay. But we recommend removing the battery for charging, as it can be placed in a safer environment in a workshop, or even on a sundeck. Charging a battery causes sulphur fumes to escape from a battery, and these can be dangerous to inhale, as well as inflammable. So charge the battery away from children, and preferably in an environment that does not contain any flammable substances.