Although nearly a century-and-a-half old, the lead-acid battery still powers conventional fuel cars

Gaston Plante. The name probably doesn’t mean anything to most people, though some may figure out its Gaelic antecedents. Yet, without this Frenchman’s invention way back in 1859, cars would not be able to run as efficiently as they do today what with all our must-have features like power windows, horn (so important in India!), indicators, head and tail lights.

However, Plante’s gift to mankind, by itself is a deadweight. Yes, I’m talking about the car battery. It’s been nearly a century and a half, but even today, the lead-acid battery still powers conventional fuel cars, be it a humble Maruti or an exalted, over-priced Mercedes-Benz. Indeed, cars would be immobile without a battery — no starting current to create that spark or heat glow plugs in petrol and diesel engines.

In 1859, Plante discovered the positive effects of a lead-acid couple, which as is evident, is the combination of lead and acid that makes up the battery. This was a very reliable and efficient combination at the time, the advantage being that both components — lead and sulphuric acid — were (and still are) easily available.

Any one who’s ever looked under a bonnet must have noticed a big, black, hard, rubber case (white polypropylene nowadays) with two terminals and thick cables connected to it. This is the much-exalted battery that I’ve been going on about. But what does a battery do in a car? Primarily, it supplies current to the starter and ignition system for cranking the engine.

Now cranking the engine is not as easy as it sounds — ask anyone who’s cranked an Ambassador with a crank rod! The battery has to overcome a number of in-built resistances in an engine — the engine’s compression ratio for one, the number of cylinders with their pistons, the entire electrical circuit resistance as well as — and this may come as a surprise — the viscosity of the engine oil. The last of these normally tends to be very thick during cold starts.

Then there is the secondary function of the battery — to be a back-up for the charging system under idle or low speed conditions like stop-start city driving conditions. The third function is to act as a voltage stabiliser for the car’s electrical system.

In a nutshell, this is how a battery does its thing. Batteries have cells in them and in each cell, there are two unlike electrodes immersed in a suitable electrolyte. Inside this cell, chemical energy is converted to electrical energy via oxidation-reduction reactions between the electrodes and the electrolyte. Both electrodes are made of lead, but different forms of it. The +ve plates are made of lead peroxide while the -ve plates are made of spongy lead. H2SO4 or sulphuric acid is the electrolyte, the medium via which electrons flow from one plate to the other during the chemical reaction.

Basically, lead becomes lead sulphate and releases electrical energy while oxygen combines with hydrogen to form water. However, the increase in water dilutes the electrolyte, causing a voltage drop. So what should be done? Passing the current in the opposite direction reverses the reaction. This reactivates the chemicals and restores power to the battery so that it can deliver power once again.

All batteries have a life span of three to five years. Beyond that, they need to be replaced. Normally batteries come as original equipment in cars. All one usually does is to go to a battery dealer and ask for a ‘Maruti ka battery’ or ‘Santro ka battery’. But in case you’re interested in what is actually beneath your car’s bonnet, this is what choosing a battery is about. Batteries have two ratings — voltage and capacity. Lead-acid cells have a 2-volt output so battery voltages are in multiples of 2V (e.g. 6, 12 and 24V).

The capacity of a battery actually implies its output delivered at a fixed voltage, for a fixed time. The fixed time depends upon the standard according to which a battery is rated. BIS (Indian) standards specify a 20-hour fixed time while Japanese standards (JIS) specify a five-hour fixed time. For example, a 50Ah battery should give 2.5Amps of current for 20 hours. Under JIS, a 24 Ah battery should deliver 4.8 Amps of current for five hours. Once a battery is put into use, the specific gravity of the electrolyte indicates the battery’s state of charge. As mentioned earlier, as the battery discharges current, more water is produced, which in turn dilutes the concentration of the acid. So the SG falls.

Today the automotive industry has moved away from hard rubber battery casings to lighter polypropylene casings. What has become common too is the maintenance-free battery because checking a battery’s water levels and topping it up is really a chore for some. Ideally, a battery today is of the fit and forget type — a fully activated, factory-charged battery, sealed against contamination that should last for over three years without any problems. However, research is ongoing to develop car batteries that are lighter, more efficient and durable. The modern version of Plante’s invention is a deadweight that just works silently.

But when a battery does act up, it can cause chaos. So it’s a good idea to have the battery and electrical system checked at least four times a year — once before each change of season as each season brings with it a different set of demands on the battery. Ideally, the person checking the battery should carry out three tests: a hygrometer test for determining the SG of battery acid, a load test to ascertain the battery’s ability to start an engine and a charge retention test. But remember, the last of these takes about seven days and is usually done to see if a battery is serviceable or not, especially if the battery has failed the first two tests.

So take care of those batteries and drive safe!

My dream car

DEEP DASGUPTA,
Cricketer

Cars are my passion, and so is driving. I love driving at breakneck speed and so fast cars turn me on. Any four-wheeler that can be driven at a killer pace is the perfect one for me.

What I need, rather demand, is speed.

I would really love to own a Mercedes or the new BMW. But the one that I am extremely passionate about is a Ferrari — it just has to be a Ferrari. Any model will do for me because I feel that all of them are simply awesome, almost out of this world.

If I do manage to own one someday, I wouldn’t like to make any alterations to it. All these cars come with customised features and naturally cater to all the demands of a car lover.

But the one problem that threatens to spoil the party for all those who love to zip, zap, and zoom is the condition of the roads in the city. Potholes and speed just don’t go!