Sure, batteries are a consumable item, but a high proportion of them fail prematurely due to poor maintenance. I blame it on the advent of the so-called low maintenance battery. Most motorists and many workshop mechanics seem to have misread low-maintenance for “no maintenance”.
Time and again, we come across regularly serviced cars with batteries having low liquid levels, or even loose terminals. The most recent case was an expensive German car that had just had a R5 000 service, and going by the look of its battery, I’ll wager that it had never been checked – ever.
Battery abuse
Abuse or neglect of the battery will show up in the following ways:
o Electrolyte leakage from the cell caps
o Powdery white electrolyte deposit, or “fuzz”, around the terminal posts
o Bulged case-ends
o Incorrect electrolyte level
o Discoloured electrolyte
o Cracked casing
o Impacted terminal posts
o Low specific gravity readings.
Most of these items can be checked visually, so a non-technical person can easily ascertain whether the battery has been a victim of abuse or incompetent servicing.
Checking the Battery
First, a caution! Batteries are filled with diluted sulphuric acid, so you should take the necessary precautions before servicing. In an emergency, flush the area with plenty of plain water. Bicarb can also be used to clean the battery case.
o Start with a visual inspection, and examine the case for cracks or leaks. It is pointless topping-up a leaking battery. Lead is harmful to humans and, therefore, obsolete batteries should be re-cycled through battery dealers who, in any event, allow a trade-in value.
o Check the ends of the battery for signs of bulging. This indicates that it has been overheated, probably because of overcharging, fast charging, or overloading.
o If the electrolyte level is too low, the top of the plates will be visible and discoloured, and the battery’s capacity permanently reduced (see Battery ratings, below). Batteries should only be topped-up using distilled water, and filled to between 6 and 15 mm above the top of the battery plates.
o If a battery is over-filled, the electrolyte will be diluted and the capacity will be reduced.
o Some areas in SA have water that’s clean enough to be used in a battery, but it’s safer to fill up with de-ionised or distilled water, because possible metal content in the water can partially neutralise the sulphuric acid.
o Discoloured electrolyte points to contaminants that will reduce the battery’s capacity.
o The terminals should be free of deposits. Dirty terminals should be cleaned with soap and water and gently scraped, then covered with a layer of petroleum jelly.
Electrolyte condition
The specific gravity (SG) is an important indicator of condition. The SG of the electrolyte changes with the state of the battery, and these changes can be measured with an hydrometer. The hydrometer is a simple glass tube containing a graduated float (sometimes coloured balls). There is a rubber bulb at one end and a tube at the other to enable acid solution to be sucked out of a cell.
There must be enough fluid for the float to float so that the reading corresponding to the meniscus (the lowest part of the surface of the water) can be noted (see sketch overleaf).
As the SG rises, so the float will rise higher out of the liquid. The specific gravity of the electrolyte should be around 1,260 for a fully charged battery, but it is usually written without the decimal point, because only the digits after the decimal point have any value in this context.
Some hydrometers have only red and green areas to show whether the SG is acceptable or not, whereas another design uses coloured balls to give the same information. We’d recommend the type that actually gives an SG reading because it can be temperature corrected, and also because ideal SGs vary according to average local temperatures. Some hydrometers are imported from countries with very different climates.
Not only will the SG determine the condition of the electrolyte, but it will also provide limited information about the charge condition of the battery. If the difference between any of the cells exceeds 50 points on a fully charged battery, the battery probably has a dead cell; this can be confirmed by consulting a battery dealer.
The SG readings marked on a hydrometer are correct at 20 degrees C, and the approximate condition of a battery can be determined from the following table:
CHARGE (%) DENSITY VOLTAGE
100 1 260 12,6
75 1 225 12,4
50 1 190 12,2
25 1 155 12,0
0 1 120 <12,0
The SG will increase by 10 units for a 15-degrees C decrease in electrolyte temperature.
The SG will decrease by 10 units for a 15-degrees C increase in electrolyte temperature.
Discharge testing
A battery dealer would apply a heavy electrical discharge test, but this cannot be done at home without special equipment. However, any time the battery struggles to turn the starter, one should get someone to operate the starter switch while you inspect the battery. Any cell that starts to boil while the battery is trying to rotate the starter is most likely dead, and the battery must be considered defective. Watch for smoke at the battery connections, and listen for a crackling sound. These are the tell-tale signs of a bad connection. Also, feel the poles; they will get hot as a result of poor contact.
Do’s and don’ts of charging
A lead-acid battery should not be stored in a discharged condition for any length of time, because it will sulphate, ie crystals will form in and on the plates preventing contact with the electrolyte. Sulphated batteries will overheat if charged, and give off a distinctive smell, similar to the smell of hydrogen peroxide.
Once a battery is badly sulphated, it cannot be recovered, and should be scrapped.
o If the battery is charged while still connected to the car, the on-board electronics may be damaged. Most domestic-use chargers are not protected and can exceed the safe voltage, or introduce damaging voltage spikes from the mains.
o The battery caps must be removed before charging to allow the gas to escape.
o Always charge batteries in a well-ventilated area, because the hydrogen gas given off is flammable and dangerous to inhale.
o Switch off the charger before connecting or disconnecting the leads to the battery. Gas arising from the charging process may explode, due to a stray spark.
If the battery needs to be disconnected from the car, remember that the codes for the radio and similar equipment may be erased, so ensure that you can get the necessary codes – or are capable of re-programming any equipment – before disconnecting the battery. One possibility of avoiding the re-programming is to connect a standby battery via an adapter lead to the cigarette lighter before disconnecting the vehicle battery. Make sure that the cigarette lighter is functioning before relying on this method of maintaining power during battery disconnection.
Charge rate:
There is no such thing as a fast charge. A discharged battery CANNOT be charged in less than 10 hours, because the battery will overheat and the plates will expand and disintegrate. The ends of the battery case will bulge outward, the amp hour capacity will be permanently reduced, and its life shortened.
The maximum charge rate that can be applied to a battery is one tenth of the A.h capacity. Any more than this charge rate will cause the temperature to rise above the maximum acceptable temperature of 55 degrees C.
The battery is considered to be fully charged when the SG and voltage do not rise any further over a two-hour time period.
The electrolyte level must be checked after charging, because the water could have boiled off during the charging process.
Connecting and disconnecting the battery:
o Two spanners should always be employed to tighten or loosen the battery terminals.
o The use of only one spanner will exert side pressure on the post, which can cause the seal between the lid and battery post to be fractured.
o The post is made of relatively soft lead, and is bonded into the battery cover. Side pressure on the post will compress the post on one side, and open up a gap on the other – this gap will leak electrolyte thereafter.
o Battery terminal clamps should not be hammered into position for the same reason.
Jump starting
This procedure should only be used in real emergencies, because the danger of damaging some of the processing units in the car is high. If you have to do it, then proceed as follows:
o Park the cars close together but not touching
o Start by connecting the positive terminal from the donor car’s battery to the positive terminal of the receiving car
o Then connect the negative terminal from the donor car to a spot on the engine of the other car, near the starter. This will ensure that the condition of the dead battery’s earth connection does not affect the charging process
o Start the engine of the donor car, and let it run for a few minutes to boost the discharged battery, then start the other car, and leave it running at idle speed only
o Before disconnecting the jumper leads after a battery boost, switch on the lights, heated rear window and heater blower at maximum speed. This is to ensure that voltage spikes arising from the disconnection will be damped
o Remove the jumper leads in reverse order
BATTERY RATINGS
Automotive batteries are rated, when new, according to their ability to deliver a fixed current for 20 hours, without the voltage (electrical unit of pressure) falling below 10,5 volts. The fixed current multiplied by 20 gives the capacity of the battery in ampere.hours (A.h). As the battery ages, the capacity reduces, because the plates and the electrolyte degrade.
The above means that a new 44 A.h battery can be discharged at a rate of 44/20 = 2,2 amps for 20 hours without the voltage dropping below 10,5 volts, whereas a 60 A.h battery can deliver 60/20 = 3,0 amps for the same period.
The larger the A.h capacity, the less discharge a battery will undergo during normal automotive use, and this normally means it will last longer. Unfortunately, the capacity is determined by the size of the plates, so there is a practical limit to what will fit into your car.
CONSTRUCTION AND CHEMISTRY
Construction
Back in 1859, when the Frenchman Gaston Plante invented the lead acid battery now so ubiquitous in cars, he probably would have been amazed to learn that 147 years later his discovery would still provide the best electrical energy storage “spark for the buck” in spite of all the sophisticated battery technology that had grown up around it. Lead acid batteries are also the most recyclable batteries, and there is such a worldwide infrastructure for this that very few are left to pollute the environment.
In simple terms, a car battery is made up of six separate sulphuric acid-filled chambers or cells. Each cell produces in excess of two volts, so that connecting them in series gives the nominal 12 volts. A cell contains sets of positive and negative lead/antimony plates, or grids.
During manufacture, both sets of plates have their grids filled with a lead oxide paste. To keep the positive and negative plates apart and prevent shorting, the plates are usually encased in a sealed porous plastic bag.
Automotive batteries are a little different from most lead acid batteries in that the plates are specially constructed to be porous so as to increase the contact area for high discharge rates while keeping the battery light and compact.
Chemistry
Before charging, both sets of plates contain lead oxide, but after adding the dilute sulphuric acid electrolyte, and charging, the material on the positive plate changes to lead dioxide (also known as lead peroxide), while the material on the negative plate changes to a spongy form of lead.
When the battery produces electricity, ie while it is being discharged, the sulphuric acid splits into hydrogen and sulphate.
The sulphate combines with the lead on both plates to form lead sulphate, and the hydrogen combines with oxygen from the lead dioxide to form the water that dilutes the electrolyte.
When the battery is charged again, the positive plate reverts to lead dioxide and the negative plate reverts to sponge lead, while the hydrogen and sulphate combine again to form hydrogen sulphide.
The practical result is that, during discharging, the electrolyte gets diluted by the water but, during charging, the acid is replenished again. Battery water has to be added from time to time, partly because of evaporation, but mainly because as a battery approaches the fully charged state, any further electrical input causes electrolysis, ie the water separates into hydrogen and oxygen.
These gases escape through the vent holes, but the mixture is quite flammable and can easily be ignited by a spark or naked flame. The reaction is so fast that the battery can explode. This is most likely to happen when a battery has been charged outside the car, and the leads are removed without switching off the power supply.
August Peterson, of Autotech, supplied us with some of the information on batteries. He offers a unique hands-on engine management training course. It’s the only training of its kind in Africa.
